The only way we can be perfected is by abiding in Christ. It is written of Christ, that "in Him" is no sin, so we cannot abide "in Him" and abide "in sin" at the same time. Jesus said be perfect as your heavenly Father is perfect. Again, the only way for this to be possible is by we abiding "in Christ" and Christ abiding "in us". Christ is One with the Father, and by Christ in us, and we in Him, we also shall be perfected in One.
John 17:22-23[SUP]22 [/SUP]And the glory which thou gavest me I have given them; that they may be one, even as we are one:
[SUP]23 [/SUP]I in them, and thou in me, that they may be made perfect in one; and that the world may know that thou hast sent me, and hast loved them, as thou hast loved me.