I believe strongly that Scripture teaches Christ was non posse peccare, “not able to sin.” His inherent righteousness is one of the attributes of His deity. His absolute hatred for sin is part of His eternal nature. He did not divest Himself of the attributes of deity in order to become man. Therefore He could no more sin than God could lie, and Scripture says plainly and repeatedly that God cannot lie. (See, for example, Titus 1:2; Numbers 23:19; and 1 Samuel 15:29. All of those texts say it is impossible for God to lie.)
Furthermore, Christ is immutable—unchanged and unchanging in His character, and the New Testament expressly declares this. Hebrews 13:8: “Jesus Christ [is] the same yesterday, and to day, and for ever.” There was nothing in Him that held any attraction whatsoever for sin. He hated sin as God hates it. He had none of the evil desires we have inherited as part of our fallen nature. Jesus could not be deceived, as Eve was. He would not yield to sin, as Adam did. In fact, although He was tempted—meaning that he was assaulted with enticements and inducements and arguments by Satan, Jesus said this about Satan in John 14:30: “The prince of this world . . . hath nothing in me.”
What about this argument that Jesus’ temptations weren’t real unless He had the possibility to sin? Look, you can put pure gold in a crucible and heat it to a white-hot temperature, and there is no possibility that it will be burned up, or that it will produce any dross. But the purity of the gold doesn’t make the heat of the flame any less hot.
If anything, Christ’s temptations were more intense, not less intense than ours, because He never sought relief from any temptation by giving in to it. He felt all the normal, non-sinful human weaknesses that you and I struggle with. Scripture says He suffered hunger, and thirst, and bodily fatigue, just like you and I do. And He surely knew what it was, under the pressure of temptation, for the pains of those infirmities to be intensified.
In fact, that is precisely what Hebrews 4:15 says: “we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin.” He bore all the natural infirmities of human flesh and endured the pressure of temptation on the night of His betrayal to the point that His capillaries burst and His sweat was mixed 11 with blood. But never, ever, did he have any attraction to sin or any desire for that which is sinful.
To say that there was ever any possibility of sin in Christ is to misunderstand the utter moral perfection of His character. I would regard it as a serious error to imagine that Christ could have sinned, because it tends to diminish the truth of His deity. Christ was non posse peccare—not able to sin, and that is true because He was God incarnate, unchanging, perfectly righteous in and of Himself, with an eternal, immutable, and holy hatred of all that is unholy.
Johnson, Phil. "Phil Johnson's Articles." The GraceLife Pulpit: The Preaching of Phil Johnson and Don Green