God appeared to Abram and said to him, "I am Almighty God. Walk before Me and be perfect" (Genesis 17:1).
If a human being cannot be perfect, why did God demand perfection of Abraham?
The entire context of the verse indicates both the definition of this perfection and the way in which it can be achieved. It is obvious that no human being can aspire to equal God's degree of perfection. What man can achieve is to live according to God's teachings and thereby live up to his own human potential; more than man's personal maximum is not possible or expected. Thus, God did not say simply, "Be perfect"; He said, "Walk before Me + and thereby you will be perfect." When a person tries to live according to the Divine teachings, that constitutes human perfection, although one is technically never perfect.
Rabbi Samson Raphael Hirsch notes that the Hebrew word for "walk" in the above verse is not telech but heshalech which implies, "Go your way in spite of opposition, not making your progress dependent on external circumstances, but being led from within yourself: Let your movement proceed from your own free-willed decisions."
The picture is now complete; human perfection can be achieved by making a free-willed choice to live according to the Divine teaching.