Matthew 27:43

“He trusts on God. Let him deliver him now, if he desires him, for he said, I am the Son of God.”

Then they also raised the question of His claim to be the Son of God (Matthew 26:63; compare Matthew 21:37; Matthew 22:2). As such surely He trusted in God? Well, if He did, let God reveal it by delivering Him now. If He is really His Son, and if God truly has any desire for Him, let Him demonstrate the fact by delivering Him. There is again an echo here of Psalms 22:8, ‘Commit yourself to the Lord, let Him deliver Him, let Him deliver Him seeing He delights in Him' (LXX has, ‘let Him deliver Him if He wants Him', which Matthew's use here suggests is based on an underlying Hebrew text).

It will be clear from this that the ideas in Psalms 22 permeate this whole narrative. See on Matthew 27:34; Matthew 27:35; Matthew 27:39 and here. It will shortly be made patent in Matthew 27:46.

It should be noted that we would expect members of the Sanhedrin to be present at the cross, not only because they would want to gloat, but also because they could hardly allow such a prominent figure, whom they had caused to be crucified, to hang in public without being themselves there to defend their position. And we would also expect the kinds of comments made here, for they were still sore at what Jesus had said to them in the High Priests' palace, and at the inscription that had been placed above Jesus' head. These comments are therefore exactly what we would expect.