Mark 15:35

‘And some of those who stood by, when they heard it, said, “See, he calls Elijah.” '

We know that Elijah was later looked on as the one who could be called on in time of religious need. It would appear from this that the idea may already have been prevalent. Or perhaps they saw the cry as a call for Elijah now to make his appearance as the forerunner for the coming of the great and terrible day of the Lord, a cry for God to act in this time of His extremity (Malachi 4:5).

We do not know who these ‘some' were. They may have been sympathetic Jewish onlookers, for word may well now have got around of what had happened to Jesus, or they may have been the Roman soldiers, auxiliaries who had a syncretistic religion which combined Jewish and foreign features and who thus knew of Elijah.