When a lot of believers become born again, they have a certain mentality: Now that I am born again, I must live right, I must live a sinless life. To their credit they do try. They try to stop the lying and the stealing and break their addictions. It lasts for a while, a week or two, possibly a month; then the old habits start rearing their ugly heads.
Does their inability to prevent themselves from falling short mean that they are not truly born again? No. What happens here is that we, believers, are living like the way the children of Israel lived. The Israelites would do their best to be good, then they would sin, God would punish them, then they would repent and the whole vicious cycle starts all over.
The children of Israel were given a set of commandments, the Law, and they were to follow these perfectly; to break one of these instructions, is to break them all. So most of them tried to do that. Their change was from without and not from within.
Ephesians 1:3 Blessed be the God and Father of our Lord Jesus Christ, who hath blessed us with all spiritual blessings in heavenly places in Christ:
Hebrews 8:12 For I will be merciful to their unrighteousness, and their sins and their iniquities will I remember no more.
God wants people whose natural response to life is what He has told them to do (like our Lord Jesus Christ whose meat was to do the will of His Father.) Not because they are afraid of punishment or because they want blessings.
So God gives us the blessings we want and says that He will remember our sins no more. Now what we wanted we have it, so we are compelled to serve and obey not not out of necessity or because of a payroll but then we serve Him because we want to. The best part of all this is that He teaches us how to serve Him.
Romans 8:3 For what the law could not do, in that it was weak through the flesh, God sending his own Son in the likeness of sinful flesh, and for sin, condemned sin in the flesh:
Romans 8:4 That the righteousness of the law might be fulfilled in us, who walk not after the flesh, but after the Spirit.
Everything illustrated above can be seen here in Paul’s letter to the church in Rome. What the Law could not do i.e. make us serve God from our hearts because we want to, God sending His Son to die for us and save us by His Grace fulfils the Law in us who walk by His Spirit.
Thus by His Spirit, the Law is fulfilled in us because now after already receiving His blessings and forgiveness, we just serve God because we want. From our hearts!! He changes us from within! Look at it this way, you owed a huge debt then a random person clears you debt and gives you a million dollars in addition. Wouldn’t you want to do anything that he asked of you? Think on these things