Who is this Spirit-Anointed Champion?
The Baptism and the Temptations go hand in hand.
Just as Israel passed through the waters and into the wilderness (and this was a baptism - 1 Cor 10:1ff), so the True Israel, Jesus, would pass through the waters of baptism and into the wilderness. Note also that the Spirit takes charge in both cases (see, for instance, Nehemiah 9:19-20. Interestingly the Spirit and the pillar are mentioned in the same breath...)
The devil's fiery arrows are aimed directly at the baptismal declaration. The Father had said:
"This is my Son, whom I love; with him I am well pleased."
The devil keeps asking, "If you are the Son of God..."
So what does it mean to be the Son of God? Well the words at baptism are reminiscent of at least three OT Scriptures.
First, Genesis 22:2
God said, "Take your son, your only son, Isaac, whom you love, and go to the region of Moriah. Sacrifice him there as a burnt offering on one of the mountains I will tell you about."
The beloved son is to be the atoning sacrifice on the holy hill.
Second, Psalm 2:6,7
"I have poured out my King on Zion, my holy hill." I will proclaim the decree of the LORD : He said to me, "You are my Son; today I have become your Father.
The beloved son is to be the King poured out like a drink offering on the holy hill.
Third, Isaiah 42:1
"Here is my servant, whom I uphold, my chosen one in whom I delight; I will put my Spirit on him and he will bring justice to the nations.
The beloved son is the suffering servant who will bring justice to the world through weakness (see the rest of the servant songs).
The devil's words in the wilderness go to the heart of Christ's identity as Son of God. Satan - ever the theologian of glory - tempts Jesus to be the Son of God who avoids sacrifice and weakness. Jesus - the true theologian of the cross - embraces this sacrifice and weakness precisely because He is the true Son of God.
As we'll see...