On The Temptation of Christ

Here is the excerpt from the Summa, Question 41, Article 1, Objection 1

Objection 1.
It would seem that it was not becoming for Christ to be tempted. For to tempt is to make an experiment, which is not done save in regard to something unknown. But the power of Christ was known even to the demons; for it is written (Luke 4:41) that "He suffered them not to speak, for they knew that He was Christ." Therefore it seems that it was unbecoming for Christ to be tempted.

Reply to Objection 1
As Augustine says (De Civ. Dei ix): "Christ was known to the demons only so far as He willed; not as the Author of eternal life, but as the cause of certain temporal effects," from which they formed a certain conjecture that Christ was the Son of God. But since they also observed in Him certain signs of human frailty, they did not know for certain that He was the Son of God: wherefore (the devil) wished to tempt Him. This is implied by the words of Matthew 4:2-3, saying that, after "He was hungry, the tempter" came "to Him," because, as Hilary says (Super Matth., cap. iii), "Had not Christ's weakness in hungering betrayed His human nature, the devil would not have dared to tempt Him." Moreover, this appears from the very manner of the temptation, when he said: "If Thou be the Son of God." Which words Ambrose explains as follows (In Luc. iv): "What means this way of addressing Him, save that, though he knew that the Son of God was to come, yet he did not think that He had come in the weakness of the flesh?"