Systematic Theology by Wayne Grudem
pg. 537 -Could Jesus have sinned?
Part 2
At this point, then, we pass beyond the clear affirmations of Scripture and attempt to suggest a solution to the problem of whether Christ could have sinned. But it is important to recognize that the following solution is more in the nature of a suggested means of combining various biblical teachings and is not directly supported by explicit statements of Scripture. With this in mind, it is appropriate for us to say: (footnote: In this discussion I am largely following the conclusions of Geerhardus Vos, Biblical Theology (Grand Rapids: Eerdmans, 1948), pp. 339-42) (1) If Jesus' human nature had existed by itself, independent of his divine nature, then it would have been a human nature just like that which God gave Adam and Eve. It would have been free from sin but nonetheless able to sin. Therefore, if Jesus' human nature had existed by itself, there was the abstract or theoretical possibility that Jesus could have sinned, just as Adam and Eve's human natures were able to sin. (2) But Jesus' human nature never existed apart from union with his divine nature. From the moment of his conception, he existed as truly God and truly man as well. Both his human nature and his divine nautre existed united in one person. (3) Although there were some things (such as being hungry or thirsty or weak) that Jesus experienced in his human nature alone and were not experienced in his divine nature (see below), nonetheless, an act of sin would have been a moral act that would apparently have involved the whole person of Christ. Therefore, if he had sinned, it woul dahve involved the whole person of Christ. Therefore if he had sinned, it would have involved both his human and divine natures in sin, then God himself would have sinned and he would have ceased to be God. Yet that is clearly impossible because of the infinite holiness of God's nature. (5) Therefore, if we are asking if it was actually possible for Jesus to have sinned, it seems that we must conclude that it was not possible. The union of his human and divine natures in one person prevented it.
But the question remains, "How then could Jesus' temptations be real?" The example of the temptation to change the stones into bread is helpful in this regard. Jesus had the ability, by virtue of his divine nature, to perform this miracle but if he had done it, he would no longer have been obeying in the strength of his human nature alone, he would have failed the test that Adam also failed, and he would have not earned our salvation for us. Therefore, Jesus refused to rely on his divine nature to make obedience easier for him. In like manner, it seems appropriate to conclude that Jesus met every temptation to sin, not by his divine power, but on the strength of his human nature alone (though, of course, it was not"alone" because Jesus, in exercising the kind of fath that humans should exercise, was perfectly depending on God the Father and the Holy Spirit at every moment). The moral strength of his divine nature was there as a sort of "backstop" that would have prevented him from sinning in any case (and therefore we can say that it was not possible for him to sin), but he did not rely on the strength of his divine nature to make it easier for him to face temptations, and his refusal to turn the stones into bread at the beginning of his ministry is a clear indication of this.
Part 3 next (after I put the kids to bed)