Here is a good explanation, "“Perfect,” in the Bible, is expressed in many ways by many translations. Perfect can be blameless, loyal, complete, mature, knowledgeable, patient, loving, and following Him. Perfect describes things such as the law of liberty (James 1:25), sacrifices (Lev. 22:21), or God’s will (Rom. 12:2). Perfection is also often linked to action: the church of Sardis is rebuked because Christ had “not found [their] works perfect” (Rev. 3:2). To the rich young ruler Jesus counsels, “If you want to be perfect, go, sell what you have … and … follow Me”
(Matt. 19:21)....
Christ’s pure attitude motivated absolute obedience resulting in a complete Oneness with the Father. That is true perfection. It is that imputed perfection that becomes the only means of our salvation. “This sacrifice was offered for the purpose of restoring man to his original perfection: yea more … to give him an entire transformation of character.”
The imparted righteousness of Christ is the work He does in us, of changing us into His image, a oneness with Him. This is what being perfect in our sphere truly means. It is to be perfectly one with Him. Our attitudes are changed, motivating obedience in us to reflect Him fully. The image He originally created us to be is reflected by our oneness with Him (see Heb. 5:8, 9). Oneness is not found by subtracting wrongs out of ourselves, for that will leave a vacuum. Rather, by addition we grab everything of Christ we can get a hold of, denying that which shadows His glory. By beholding we become like Him and are changed into His glory. We will not only be His image but will be one with Him...."
http://archives.adventistworld.org/article/673/resources/english/issue-2009-1012/perfection