Just because we see does not mean that we will believe because there is a spiritual aspect to this sort of seeing and believing. This passage indicates that "His own" showed not even a flash of recognition as to His true identity.
Consider the incongruity of this. We frequently hear of personalities in the public eye affecting some kind of a mode of dress or lifestyle that will set them apart and make them instantly recognizable. In this regard, compare Jesus Christ, the most unique Personality that ever lived in the history of mankind! He was a one-of-a-kind, the only human who ever lived life sinlessly. Yet, even those of His generation who saw Him could not identify Him, God in the flesh!
This suggests that one must be predisposed to believe, to have the ability to "see." It is interesting to note that, to those who exercised this faith, "He gave the power [right, authority, ability] to become the children of God" (verse 12). Only those who "see" and then "receive" Christ can enter into a relationship with God that results in nothing less than the creation of a new being.
John W. Ritenbaugh
Do You See God? (Part One)
"Not of blood" refers to the fact that there is no physical generation process by which we can become sons of God.
"Nor of the will of the flesh" indicates that we were not looking for God—we did not know what to look for. We knew about a lot about gods ("there are many gods," Paul says in I Corinthians 8:5), but we did not know what the God of the Bible was like. That is what we have to come to know. That is where eternal life resides—in knowing God (John 17:3). We did not know Him.
We did not know Him because we did not know what to look for. Even though we may have been searching for "God," we were not really searching for the God of the Bible, as we had no idea what to look for. We would never have looked for a God who commanded the keeping of the Sabbath or the holy days. Those are "Jewish." Our minds have been prejudiced in many different directions. We never would have looked for the God of the Bible.
John is showing it in another way—that we were not born by physical generation. We did not come to know God through any act of our own will, but rather it was something that came as a gift from God entirely.
John W. Ritenbaugh
John (Part 3)