No one has ever gone into heaven except the one who came from heaven—the Son of Man. (NIV)
The Jews would not have taken John’s words to mean that Christ “incarnated.” It was common for them to say that something “came from heaven” if God were its source. For example, James 1:17 says that every good gift is “from above” and “comes down” from God. What James means is clear. God is the Author and source of the good things in our lives. God works behind the scenes to provide what we need. The verse does not mean that the good things in our lives come directly down from heaven. Most Christians experience the Lord blessing them by way of other people or events, but realize that the ultimate source of the blessings was the Lord. We should apply John’s words the same way we understand James’ words—that God is the source of Jesus Christ, which He was. Christ was God’s plan, and then God directly fathered Jesus.
There are also verses that say Jesus was “sent from God,” a phrase that shows God as the ultimate source of what is sent. John the Baptist was a man “sent from God” (John 1:6), and it was he who said that Jesus “comes from above” and “comes from heaven” (John 3:31). When God wanted to tell the people that He would bless them if they gave their tithes, He told them that He would open the windows of “heaven” and pour out a blessing (Mal. 3:10 – KJV). Of course, everyone understood the idiom being used, and no one believed that God would literally pour things out of heaven. They knew that the phrase meant that God was the origin of the blessings they received. Still another example is when Christ was speaking and said, “John’s baptism—where did it come from? Was it from heaven or from men?” (Matt. 21:25). Of course, the way that John’s baptism would have been “from heaven” was if God was the source of the revelation. John did not get the idea on his own, it came “from heaven.” The verse makes the idiom clear: things could be “from heaven,” i.e., from God, or they could be “from men.” The idiom is the same when used of Jesus. Jesus is “from God,” “from heaven” or “from above” in the sense that God is his Father and thus his origin.
The idea of coming from God or being sent by God is also clarified by Jesus’ words in John 17. He said, “As you sent me into the world, I have sent them into the world” (John 17:18). We understand perfectly what Christ meant when he said, “I have sent them into the world.” He meant that he commissioned us, or appointed us. No one thinks that we were in heaven with Christ and incarnated into the flesh. Christ said, “As you have sent me, I have sent them.” So, however we take the phrase that Christ sent us, that is how we should understand the phrase that God sent Christ.
Buzzard, pp. 154-157
Norton, pp. 246-248