By now it should be obvious that this business of spiritual growth is somewhat daunting. That is not to say that the Bible is wrong about the difficulty of obeying God. There is a system of teachings in the Bible that we should take note of here.
3 For this is the love of God, that we keep His commandments. And His commandments are not burdensome.
1 John 5:3 (NKJV)
30 For My yoke is easy and My burden is light.”
Matthew 11:30 (NKJV)
13 “Enter by the narrow gate; for wide is the gate and broad is the way that leads to destruction, and there are many who go in by it. 14 Because narrow is the gate and difficult is the way which leads to life, and there are few who find it.
Matthew 7:13-14 (NKJV) (compare Luke 13:23-24)
24 Then Jesus said to His disciples, “If anyone desires to come after Me, let him deny himself, and take up his cross, and follow Me.
Matthew 16:24 (NKJV)
These statements do not contradict each other. On the one hand, we are created for God, so obeying God is actually living a truly human life. On the other hand, we have sin in our flesh, so we have a natural drive to disobey God. That is to say that we are always in a war within ourselves to determine which drive or nature we will yield ourselves to.
29 Truly, this only I have found:
That God made man upright,
But they have sought out many schemes.”
Ecclesiastes 7:29 (NKJV)
16 I say then: Walk in the Spirit, and you shall not fulfill the lust of the flesh. 17 For the flesh lusts against the Spirit, and the Spirit against the flesh; and these are contrary to one another, so that you do not do the things that you wish. 18 But if you are led by the Spirit, you are not under the law.
Galatians 5:16-18 (NKJV)
Every human being born into this world possesses a corrupted human nature, that is, a human nature that is soiled with ungodly desires. This corruption exists in our physical bodies that derived from our parents and ultimately from Adam, the first of our race. This corruption came into being when Adam chose to disobey God and eat of the fruit of the tree of the knowledge of good and evil that the Lord had forbidden for him and his wife Eve. In the course of our study, we will eventually discuss this in greater detail. For now, suffice to say that when Adam sinned, the Lord made it such that every human being born of male seed inherits the corruption that was in Adam’s flesh from eating the fruit. This is the gist of Paul’s teaching in Romans 5:12-19. 
18 For I know that in me (that is, in my flesh) nothing good dwells; for to will is present with me, but how to perform what is good I do not find.
Romans 7:18 (NKJV)
Whereas our physical bodies have sin in them, our spirits are pristine (Romans 7:22). We still have a conscience or a moral compass such as Paul alludes to in Romans 2:14-15. Of course, we can completely ignore this moral compass and live entirely according to the dictates of our flesh, but this does not mean that we don’t have another bent of nature. We do. While we were unbelievers, we were aware of this tug from our spirits. It is in no small measure due to it that we became believers in the first place. As believers, we are no less aware of it. Having become alive to God as believers and possessing the Holy Spirit means that our conscience is even more active (and more accurate too as we learn the truth of the Bible) than before.
The pull of our flesh and the opposite draw of our spirit together mean that we will find the business of spiritual growth challenging. When we seek to do the right thing, our own bodies will weigh in with its “needs” and insistent desires, opposing that effort that we might be wishing to make or are already making. This is a very real battle for us. If it were not, all believers would be spiritually mature and tremendously productive for the Lord. Obviously, we aren’t all spiritually mature, much less productive. In general, throughout history, the challenge of putting our own desires and worries aside in order to follow the Lord has proved too hard for the majority. That is why so few throughout history have even been saved. Even fewer have gone on to grow spiritually. 
Our flesh is only one thing that we have to deal with. Satan himself and the world (that is, the spiritual system that he fashioned all around us through the lies that he has sold to the sons of disobedience) are opposed to our good desire to grow spiritually and be fruitful for the Lord. We are mocked and persecuted in one way or another for preferring to follow the Lord rather than continue to participate in the wicked ways of this present world. We suffer spiritual opposition from Satan through temptation to sin and through other spiritual sufferings of which we may not be fully aware.
4 They are surprised that you do not join them in their reckless, wild living, and they heap abuse on you.
1 Peter 4:4 (NIV)
7 And lest I should be exalted above measure by the abundance of the revelations, a thorn in the flesh was given to me, a messenger of Satan to buffet me, lest I be exalted above measure.
2 Corinthians 12:7 (NKJV)
These oppositions are not to be underestimated. Satan is deeply invested in our failure at being believers. He works to prevent unbelievers from becoming believers and to prevent believers from becoming serious with our faith so that we remain susceptible to falling away into apostasy. If he fails at preventing these things, he reacts in anger toward those who do become spiritually mature and are being fruitful for the Lord. The world is his ally in this and so is our flesh. This means that there will always be pain to deal with if we decide to walk humbly with God, learning His Truth, believing and obeying it.
33 These things I have spoken to you, that in Me you may have peace. In the world you will have tribulation; but be of good cheer, I have overcome the world.”
John 16:33 (NKJV)
Why then should we persevere? Why should anyone pursue spiritual growth given all the trouble associated with it? As we have seen in many of the passages already posted, the trouble is not the only thing that we are assured that we will have. We are also assured of the comfort of the Lord in the midst of all of our troubles right here on earth. The Lord gave us His Word that all the loss that we suffer in following Him in this world will be more than compensated by Him (Mark 10:28-31) in this world also. For example, if our family and friends ostracize us because of our choice to follow Him, He promises that we will have a new family and friends that will accept us in this world (Psalm 68:6). This is fulfilled in our finding a home among fellow believers who love His Truth. In this way, the Lord offers us His comfort. In this world, the Lord comforts us with His Peace (John 16:33) and with His Joy (John 16:24).
We have other motivation for pursuing spiritual growth too. Not only does the Lord promise that all that we give up in this world will be made up to us in the perfect way, He also promises us that we will be rewarded in the world to come in magnificent ways for our sacrifices here. There are rewards in eternity that answer to all of our works here on earth. The Lord Jesus Himself is our prime example in this.
2 . . . Jesus, the author and finisher of our faith, who for the joy that was set before Him endured the cross, despising the shame, and has sat down at the right hand of the throne of God.
Hebrews 12:2 (NKJV)
5 Let this mind be in you which was also in Christ Jesus, 6 who, being in the form of God, did not consider it robbery to be equal with God, 7 but made Himself of no reputation, taking the form of a bondservant, and coming in the likeness of men. 8 And being found in appearance as a man, He humbled Himself and became obedient to the point of death, even the death of the cross. 9 Therefore God also has highly exalted Him and given Him the name which is above every name, 10 that at the name of Jesus every knee should bow, of those in heaven, and of those on earth, and of those under the earth, 11 and that every tongue should confess that Jesus Christ is Lord, to the glory of God the Father.
Philippians 2:5-11 (NKJV)
9 But we do see Jesus, who was made lower than the angels for a little while, now crowned with glory and honor because he suffered death, so that by the grace of God he might taste death for everyone.
Hebrews 2:9 (NIV)
Every human being understands reward motivation. We all experience the motivation that comes from looking forward to some reward after we have done the work involved in getting to the reward. We do schoolwork so that we can get good grades and secure well-paying careers. We work at our jobs so that we can get our pay packets that provide for our lifestyles. Even the criminally minded among us must go to the trouble of committing crimes at considerable risk to their own lives and wellbeing in order to gain some reward that they deem worthy of the risk.
God built this into us. It is part of human nature to desire a reward for the things that we work at or endure. This is what gets us going at all. Our lives on earth are hard, whether we are believers or not, whether we choose to be serious about the Lord and His Truth or not. Therefore, there is always deep in our hearts that question, “what’s in it for us?” It may not sound right to us that we do feel this way toward the Lord especially considering how much He already did for us and how much He is always doing for us, but it is to His glory that we should desire the rewards that He has prepared for those who love Him.
6 And without faith it is impossible to please God, because anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him.
Hebrews 11:6 (NIV)
31 But seek his kingdom, and these things will be given to you as well.
32 “Do not be afraid, little flock, for your Father has been pleased to give you the kingdom. 33 Sell your possessions and give to the poor. Provide purses for yourselves that will not wear out, a treasure in heaven that will never fail, where no thief comes near and no moth destroys. 34 For where your treasure is, there your heart will be also.
Luke 12:31-34 (NIV)
One way to think about this is that if we were employers, we would want our employees to value our rewards and incentives enough to work hard at earning them. The same applies to even more “altruistic” relationships. We rejoice in having children who value our approval, in having friends who look forward to our pride in their achievements. It is no different with God, only so much better, so much purer.
2 My Father’s house has many rooms; if that were not so, would I have told you that I am going there to prepare a place for you? 3 And if I go and prepare a place for you, I will come back and take you to be with me that you also may be where I am.
John 14:2-3 (NIV)
The Lord gains nothing at all from what we do. It is entirely of His Grace that we get to participate in His Plan for creation. What He does in giving us a role to play is out of His Love for us to grant us an opportunity to share in His glory (John 17:22; Romans 8:17,32).
So the Lord has prepared eternal rewards for us according to our response to His call that we should grow spiritually and bear lasting fruit for Him. They are meant to be our motivation to work at the things that He has called us to (Philippians 3:14). These rewards are graduated according to our spiritual attainments in this life (2 Corinthians 5:10). Every single thing that we do for the Lord that is truly in keeping with God’s Will will be rewarded (Matthew 10:42). There are also different levels of reward, some greater than others. There are the basic level of rewards, then the crown of righteousness (2 Timothy 4:8) followed by the crown of life (James 1:12; Revelation 2:10) and finally the crown of glory (1 Peter 5:1-4). There are special cadres of achievers too who in addition to winning the highest level of rewards are also selected into special groups of performers who went above and beyond expectation.
None of these rewards is a mean thing. Even the very least of the rewards that God has prepared for us is eternal in nature (Matthew 6:20). That quality of permanence in itself alone makes these rewards of infinitely greater value than anything that this impermanent world can offer. Even if we had all the comforts of this life and none of its pain, we would still die and lose our grip on all of it. The least reward of eternity, on the other hand, will never be lost again through death once we receive it. It will always be ours. Add to this the fact that this life is full of pain and sorrow. There is no good thing in it that does not carry some trouble with it. In other words, even its good things are not perfect. The rewards that God has prepared for those who love Him, on the other hand, are utterly good. There is no pain that comes with it. Rather we are promised that He will wipe away every tear from the eyes of those who love Him (Revelation 21:4).
God-willing, we will come back to a fuller discussion of these rewards. It suffices here to announce to us that this is what the Lord calls us to, that this is our motivation for enduring the difficulties and challenges of spiritual growth.
8 What is more, I consider everything a loss because of the surpassing worth of knowing Christ Jesus my Lord, for whose sake I have lost all things. I consider them garbage, that I may gain Christ 9 and be found in him, not having a righteousness of my own that comes from the law, but that which is through faith in Christ—the righteousness that comes from God on the basis of faith. 10 I want to know Christ—yes, to know the power of his resurrection and participation in his sufferings, becoming like him in his death, 11 and so, somehow, attaining to the resurrection from the dead.
12 Not that I have already obtained all this, or have already arrived at my goal, but I press on to take hold of that for which Christ Jesus took hold of me. 13 Brothers and sisters, I do not consider myself yet to have taken hold of it. But one thing I do: Forgetting what is behind and straining toward what is ahead, 14 I press on toward the goal to win the prize for which God has called me heavenward in Christ Jesus.
Philippians 3:8-14 (NIV)