In a number of posts (e.g., "The Reality of Christ's Humanity: Was it possible for Jesus Christ to sin?"), I have argued that, for Jesus to have been truly human, and to have been truly tempted like we are, it had to be possible for him to sin, not just for him to be tempted. If not, this makes a charade of His temptation in the wilderness (Mark 1:12-13; Matt 4:1-11; Luke 4:1-13), and makes nonsense of Heb 2:17-18:
Therefore he had to become like his brothers and sisters in every respect, so that he might be a merciful and faithful high priest in the service of God, to make a sacrifice of atonement for the sins of the people. Because he himself was tested by what he suffered he is able to help those who are being tested. (NRSV [click here for a discussion of the use of ιλασκεσθαι and its soteriological significance])
Consider also the words of Heb 4:15:
For we do not have a high priest who is unable to sympathise with our weaknesses, but we have one who in every respect has been tested as we are, yet without sin (πάντα καθ᾽ ὁμοιότητα χωρὶς ἁμαρτίας). (NRSV)
Here, the author of Hebrews states that Christ was made like us in every respect except for the fact he did not commit sin, not in every respect except the inability to sin. The only way truly have been tempted necessitates that one has the ability to sin.
I just recently came across the following quote on the true humanity of Jesus from Max Thurian that, while he is a Trinitarian and holds to the Hypostatic Union which, ultimately, makes nonsense of Christ’s humanity ("[Christ] is, in two distinct natures, divine and human, one single person" [p. 66]; for a refutation of this doctrine, see the section, “The Hypostatic Union Examined” of this paper), he is spot-on on the necessity of Jesus being truly human, not just the second person of the Trinity who has impersonal human nature:
If God was truly to share our humanity he could not simply live among us under an outward appearance of humanity. Then he too would have remained remote and we would not have felt involved with him, through his human example and his liberation of mankind. So God's will was to become man he became a man like ourselves, except for sin. The person of the Son was incarnate in Jesus of Nazareth, the son of the Virgin Mary, according to the Father's will, by the action of the Holy Spirit. (Max Thurian, Our Faith: Basic Christian Belief [trans. Emily Chisholm; Taizé, France: Les Presses De Taizé, 1978] 66)
