John Gill Commentary Matthew 27:43

"He trusteth on God; let him deliver him now, if he desireth him: for he said, I am the Son of God." — Matthew 27:43 (ASV)

He trusted in God
That is, he pretended to claim an interest in him, to be high in his favour and esteem, and to have great faith and confidence in him:

let him deliver him now ;
directly, from the cross, and the death of it:

if he will have him ;
or if he is well pleased with him as his own Son, or delights in him as such, and will show him any favour and good will; see (Psalms 22:8) , where are these very words, and which are predicted should be said by these men to Christ; and are a wonderful confirmation of the truth of that Psalm and prophecy belonging to him:

for he said, I am the Son of God ;
not only in his ministry, but he had said so in their grand council, before them all.