Summary: Most of us as Christians are so comfortable counting on our long year of salvation and probably service in the house of God yet the Almighty God whom we claim to be serving is so disappointed in our relationship with Him. Grow your relationship with Him.
There is a reason for you to be perfect, and that is because I am the Almighty, the God who is perfect in all things. However, you cannot become perfect by any other means except by growing your relationship with Me.
Those were the words of God to Abraham in Genesis 17:1, fifteen years after he was called out of his kindred. We can therefore conclude that Abraham was still the same person even after he became "born again" and remained so for fifteen years. He was following God at his own pace, relying basically on his instinct and sense of judgment rather than growing his relationship with the Almighty by walking before Him who had called him.
His lengthy years of experience as a "Christian" was no way commensurate to his spiritual growth. It was just like the case of the Hebrews who had a stunted spiritual growth and remained learners when they ought to have become teachers (Heb 5:12).
God was very explicit in this conversation with Abraham and He made it clear to him that if He must remain his God and if he would expect something tangible as the outcome of their relationship, there was an urgent need for him to abandon his old manners of approach in dealing with Him and embrace His.
This is very well applicable to most of us Christians today; we have a very long year of salvation experience yet we are spiritual babes. God has patiently waited for us to abandons our ways for His but we did not give a damn. We are just too comfortable being saved. God is calling on us at this time just as He did to Abraham to come out of the euphoria of salvation into the reality of perfection which can only be attained by growing our relationship with Him.
He's the Almighty God and He's the only one Who can help shed imperfection from our lives as we get closer to Him, trust more in Him, become more indoctrinated in His word and depend more on Him rather than our instinct, skills, knowledge, achievements, etc.
Simply put, God wants more of you to bring out more of Himself in you.