He was sinless because he was the friend of sinners!
"This fellow welcomes sinners and eats with them" (Luke 15:2).
Jesus' sinlessness was anything but obvious. The sign of it was not heroic moral purity but a life that called his purity into question. His friends and associates were not the good church people of this day. They were his enemies, not because he rejected them but because they rejected him. His friends were political revolutionaries (the Zealots), dishonest business people who were also traitors to their nation (the tax collectors), immoral women, social outcasts, and half-breeds... In this way he was for his fellow human beings as they really are- guilty, needing forgiveness, acceptance, and help. In this way he was obedient to God and fulfilled the task God had given him to do- not to minister to well people who do not need a doctor but to sick people who do; not to call the righteous but sinners (Matt. 9:12-13). His sinlessness was his willingness to be sent "in the likeness of sinful flesh" (Rom. 8:3-4) in order to overcome the broken relationship between God and humanity and between human beings themselves. It was the willingness of the one who "knew no sin" to be made sin for our sake (2 Cor. 5:21).
Jesus was sinless because, in perfect obedience to God and perfect love for his fellow human beings, he was willing to risk his good name and his "moral integrity" to be with and for undeserving, unworthy, sinful people.
-what I came across while doing homework this evening