I'm only human. This is something we say or hear said when explaining a wrong done or when exhibiting a flaw in our character. I'm only human. It's another way of saying, "I'm not perfect," or "I'm frail." I'm only human. It's another way of saying, "I'm a sinner."
But to equate our humanity with sin is quite problematic from a theological standpoint. Nowhere does the Bible equate sin with humanity. Nowhere does the Bible state that the problem with humanity is that it is human. God created us human. The problem, the Bible insists, is our sin, which is something entirely different from our humanity. Our sin is not a revelation of our humanity; rather it demonstrates that we are less than human, we are not what God created us to be.
The Christian belief in Incarnation is an affirmation of our humanity. Jesus was fully human. The fact that he was without sin, as the Book of Hebrews claims (Hebrews 4:15), is what makes Jesus fully human. You and I are human, but our sin will not allow us to put the adverb "fully" in the description. Jesus Christ has come to change that. Salvation in Jesus Christ is the work by which God intends to restore our humanity.
Only a fully human (and fully divine) Jesus can restore the cracked image of God in us and return us to the full height of our humanity, the humanity God intended for us. Without this salvation, we will hopelessly remain less than human.