why is this step so important
Confession - 1 John chapter 1 tells us how important it is to confess our sins to God; in verse 9, If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
Did you notice the key words confess, faithful, forgive and cleanse, and not just some of our confessed sins, but all unrighteousness.
It's important that we beleive and confess. - Romans 10 explains in verse 10, For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation. God very plainly tells us to speak verbly with our mouth, confess, believe from your heart in his righteousness, and go tell others. After all, this is an exciting event, you just accepted Christ!
You are now Born Again! - 1 Peter 1:23 Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever.
Don't hide it, be excited and spread the victory. Don't grieve God.
Ephesians 4:30 And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption.
Romans 6:22 But now being made free from sin, and become servants to God, ye have your fruit unto holiness, and the end everlasting life.