http://www.ccel.org/ccel/mcgarvey/gospels.v.ii.html
And the devil said unto him, If thou art the Son of God…
Jesus is tempted in the wilderness by Satan, and two of his temptations carry this phrasing. In both cases, Jesus answered the second half (turn these stones into bread, throw yourself down), but he doesn’t deal with the first half – “if you are the Son of God”. So why is Satan asking these questions? Is it because Satan isn’t sure? Is it because Satan is attempting to plant seeds of doubt in Jesus’ mind about his own divine nature? Because Satan’s question is essentially this: prove that you are the Son of God by doing this. And Jesus’ answer is, I’m not going to do “x”, and here’s why. The proof of his divine lineage is left unproven.
Now, this temptation comes right after Jesus is baptized by John, and the Spirit of God descends upon him and the Voice of God says, “This is my son.”
Why does the devil then attack that point? I don’t have a good answer for that.
But remember this as well: nobody was with Jesus in the wilderness. The reason that we have this story is that Jesus told his disciples and it became a story that they used, probably for illustration purposes. So Jesus told his disciples that Satan questioned his divine nature, and he sidestepped the question. What’s the meaning of that? Jesus seems to want his disciples to discover for themselves that he is the Son of God, instead of telling them at every opportunity.