There is a sense in which the perfection of Jesus is simply assumed. Hebrews 4:15 says, "We do not have a high priest who is unable to sympathize with our weaknesses, but one who is in every respect has been tempted as we are, yet without sin." There is a reason for it...
To help you understand the nature of why Jesus needed to be sinless, perfect in all His ways, I want to take you into a courtroom. Imagine for a moment that you are guilty of a crime - a capital crime - and your life is now subject to the full extent of the law. The judge hands down the sentence and you are going to be led away to your final end. Then... one steps up and declares that he will take your place!
But what if that person was guilty of the same crime? There is no way he could take your place for he, himself, must be punished for his own crime. He could never be your substitute and bear your punishment for he must endure his own.
Do you see? Every person on the planet is guilty before God of a crime called sin. The ONLY person who could ever take their place, be the substitution for all mankind, is someone who is perfect. If Jesus had been guilty of any sin He could never be the propitiation for such sin for He must then be punished for His own. But Jesus IS perfect in all His ways, He is without sin and can be the sacrifice for anyone... anyone who believes.
© 2015 Michael Duncan
If you are looking for a study to help you understand your life if Christ, I encourage you to pick up the study guide: "Starting Out: A Study Guide for New Believers"
available at Amazon.com http://www.amazon.com/Starting-Out-Study-Guide-Believers/dp/1482694328/