Christ being fully man and fully God is distinct from sinner or Christian. Jesus was the son of man, yet without sin. If a Christian identifies with Jesus, he identifies with His righteousness in flesh and spirit, since the flesh is crucified with Christ, and it is no longer I who live, but Christ who lives in me. My framing doesn't imply, "if you sin you would lose your salvation." It implies that a Christian can't identify with Jesus and sin at the same time. The scripture is clear, that if you confess your sins, he is faithful and just to forgive your sins and cleanse you of all unrighteousness.