Jesus Christ, during His days in the flesh, was holy, harmless, undefiled, and separate from sinners (Heb. 7:26). To suggest that He had a nature subject to sin is nothing short of blasphemy.
On the other hand, depraved men are capable of sin because each one has a mind that is ready to receive an evil suggestion. Man is tempted when he is drawn away by his own lust (James 1:14). The Greek word for “lust” is epithumia. It means lust, desire, craving, or longing. A person is tempted when he is enticed by his own craving for that which is forbidden or unlawful.
No one who understands the Biblical teaching concerning the Person of Jesus Christ could entertain a thought that He could desire the unlawful or forbidden. That is why James said, “God cannot be tempted with evil” (James 1:13).
Evil that is in man is his own. Within man’s heart are evil desires. They are there by nature. The Devil does not introduce them. All Satan does is find out where man is most vulnerable and bombard him with things he craves. The evil suggestion admitted into one’s mind will grow in strength because of the evil desire already resident in man unless it is resisted by grace.
This is the question: Did Satan ever find a weak spot in Jesus Christ? Since there was no weakness in Him, He could never be solicited to do anything contrary to His holy character. Therefore, Jesus Christ could not be tempted with evil (James 1:13). It must be understood that evil exists in man before it comes forth from him in action. On the other hand, there was no evil in Christ. He could not be tempted by any suggestion or solicitation from without.
To say that Christ could have sinned as to His human nature but not as to His Divine nature forces one to conclude that there was a conflict between His two natures. This was impossible because His human nature was united to His Divine Person. Thus, there was never any conflict in Christ as there is in the Christian (Rom. 7:15-25).
There are several things to consider in the solicitation to sin. First, there is the attraction by the suggestion of something that is desirable. That which is desired is forbidden. In order for the tempted to have what has been suggested, he must ignore a Biblical precept.
One cannot deny that the Devil made some offers to Christ in the wilderness. Neither can one deny that the eternal Son was eternally aware of every detail of the offers made by the Devil. But it is nothing short of blasphemy to entertain the thought that the Son of God wanted anything offered by the Devil. Some religious leaders are so full of iniquity that they maintain that the human nature of Jesus Christ was as fallen and rebellious as their own. The Bible teaches that the human nature is corrupt from head to foot (Is. 1:6), but it is a sign of spiritual blindness to imagine that Christ’s human nature was tainted with depravity. Christ’s human nature is called “that holy thing” (Luke 1:35).
~Excerpts, E.W. Best, Christ Could Not Be Tempted
Another way of stating this: Jesus Christ the Lord was not some hypothetical sinner. That is blasphemous. Moreover it would necessitate God having a plan B in cause Jesus did sin. That too, is blasphemous.