Matthew 4:3-4, And the tempter came and said to Him, “If You are the Son of God, command these stones to become loaves of bread.” But He answered, “It is written, ‘Man shall not live by bread alone, but by every word that comes from the mouth of God'” (cf. Deuteronomy 8:3).
Satan didn’t test Jesus out of doubt to see if Jesus really is the Son of God. Certainly, he knew whom he was messing with. But in his foolishness, he thought he could trick the Son of God in the desert just as he tricked Adam and Eve in the garden. He knew Jesus’ divinity—that He is the Son of God. But he thought he could trick Him in His humanity. If he could just trick the Son of God into sinning, he would thwart God’s salvific plan for humanity. But Jesus, being the Son of God, saw through the Devil’s trickery and did what we could not in the garden and cannot do today without His grace—trust and rely on the Word of God alone.
Jesus Christ fulfilled in the desert what we were incapable of fulfilling in the garden and continue to fail today apart from His grace. Thus, what do we do when the Devil tempts us that we are lost? Believe and trust the Word of God, which says, “If you confess with your mouth that Jesus is Lord and believe in your heart that God raised Him from the dead, you will be saved” (Romans 10:9). Believe and trust in this Word, which is for you. For “confess” is not the mere saying of the words, “Jesus is Lord.” To confess (ὁμολογέω, homologéō) in this sense is both to share a common view and to concede something to be true. Thus, by faith, when we confess Jesus to be Lord of our lives and all creation, we are in agreement with other Christians and we believe it to be true with all our hearts. This is faith that saves. Therefore, trust in this Word. God said it, therefore it is.