The impeccability of Christ by virtue of his impeccable divine nature united to his human nature has nothing directly to do with how he resisted temptation and how it was that he did not sin. Yes, Christ was impeccable, but his impeccability is quite literally irrelevant to explaining his sinlessness. The common evangelical intuition seems to be this: if the reason Christ could not sin is that he is God, then the reason Christ did not sin must likewise be that he is God. My proposal denies this symmetry and insists that the questions of why Christ could not sin and why he did not sin require, instead, remarkably different answers.
To understand better the distinction here invoked between why something could not occur and why it did not occur, consider with me two illustrations. First, imagine a swimmer who wants to attempt breaking the world’s record for the longest continuous swim (which, I’ve read, is something over 70 miles). As this swimmer trains, besides his daily swims of 5 to 10 miles he includes weekly swims of greater distance. On some of the longer swims of 30 and 40 miles, he notices that his muscles can begin to tighten and cramp a bit, and he becomes worried that in attempting to break the world record, his muscles may cramp severely and he could then drown. So, he consults with friends, and they decide to arrange for a boat to follow along behind the swimmer 20 or 30 feet back, close enough to pick him up should any serious problem arise but far enough away so as not to interfere with the attempted historic swim itself. On the appointed day, conditions being just right, the swimmer dives in and begins his attempt at breaking the world record. As he swims, the boat follows along comfortably behind, ready to pick him up if needed. But no help is needed; with determination and resolve, the swimmer relentlessly swims and swims and swims, and in due time he succeeds in breaking the world record.
Now, consider two questions: (1) Why is it that in this record-breaking event the swimmer could not have drowned? The answer is that the boat was there all the while, ready to rescue him if needed. But (2) Why is it the swimmer did not drown? The answer is that he kept swimming! Notice that the answer to the second question has nothing at all to do with the boat, i.e., it has nothing to do with the answer to the first question. In fact, if you gave the answer of “the boat” to question 2, the swimmer would be both astonished and dismayed. It simply is not true that the swimmer did not drown because the boat was there. The boat, quite literally, had absolutely nothing to do with why the swimmer did not drown. Furthermore, although the swimmer knew full well that he could not drown due to the boat’s following along behind him, that knowledge had nothing to do with why he did not drown, since he also knew that if he ever relied on the boat, his mission of breaking the world record would be forfeited. So although he knew that he could not drown due to the boat, he also knew that he could only accomplish his goal by swimming as if there were no boat there at all. . . .
As one considers again the temptations of Christ, it seems that one should rightly hold that the theanthropic Jesus could not sin because he was God. But this does not necessarily answer the question of why he did not sin. And, in fact, the answer Scripture suggests to us is this: Jesus did not sin, not because he relied on the supernatural power of his divine nature or because his divine nature overpowered his human nature, keeping him from sinning, but because he utilized all of the resources given to him in his humanity. He loved and meditated on God’s Word (consider again the significance here of Psalm 1 being the first and opening psalm, pointing obviously to Christ); he prayed to his Father; he trusted in the wisdom and rightness of his Father’s will and Word; and, very significantly, he relied on the supernatural power of the Spirit to strengthen him to do all that he was called upon to do. Jesus lived his life in reliance on the Spirit so that his resistance to temptation and his obedience to the will of the Father took place through, not apart from, the empowerment provided him as the second Adam, the seed of Abraham, the son of David. Recall again Peter’s claim that God anointed Jesus “with the Holy Spirit and with power,” and that he went about doing good (the moral life and obedience of Christ) as well as healing all who are oppressed by the Devil (the miracles he performed), “for God was with him” (Acts 10:38). Although he was God, and although he was impeccable as the God-man, he resisted temptation and obeyed the Father not by his divine nature but by the power of the Spirit who indwelt him.