Romans 4:5 (NKJV) 5 But to him who does not work but believes on Him who justifies the ungodly, his faith is accounted for righteousness,
The bible says in Hebrews 10:1, "For the law, having a shadow of the good things to come..." Before the sacrifice of Jesus on the cross the only way to achieve righteousness was to obey the law. This verse then goes on to say that the law could never make any man perfect.
The Bible says in Deuteronomy 30:14, "But the word is very near you, in your mouth and in your heart, that you may do it." The "word" is referring to the laws of God. Take notice that the verse ends with "that you may do it". If you read on to verse 16 you will see the benefits of obeying the law are blessings from God. God was telling us that if we could obtain righteousness then He could bless us.
After Jesus died on the cross the apostle Paul quoted this verse to the Romans. The Bible says that He put it this way; "...The word is nigh thee, even in thy mouth, and in thy heart: that is, the word of faith, which we preach." (Romans 10:8 KJV) Notice that that Paul replaced the words "that you may do it" with the words "which we preach". We no longer have to work for righteousness we just preach it. This means you declare that God gave you His right standing to obtain His blessings.
The Bible says in John 3:17, "For God did not send His Son into the world to condemn the world, but that the world through Him might be saved." God is not a condemning God. He can only change you if nothing comes between you and Him. In Jesus there is no condemnation. (Romans 8:1) God is all about freedom. The Bible tells us in Romans 6:14, "For sin shall not have dominion over you, for you are not under law but under grace."
In the Old Testament the sin of man separated him from God. In the New Testament we simply declare God's righteousness as a gift from God and nothing can come between us. If you are not separated from God then He can work in you. When God works in you He makes changes. He changes your unhealthy desires and just replaces them with healthy ones. You don't change because you have to, you just change.
God is all about releasing us from bondage. The more we involve Him in our life, the more He can do in us. To involve God, spend time reading His word and He will talk to you. You need to talk to Him too. Talk to Him even if you are committing sin. He knew you where going to sin before you even thought about it. He doesn't love you less because of it.
So relax, and accept the gift of freedom provided by grace. Let God do the work. Don't let anything stop you from talking with Him.