Hi simpleman,
I looked up the commentary for Matthew 27 (NIV) from the "BibleGateway.com" and this is what it say:
"The Father Vindicates His Murdered Son (27:50-53) Elijah did not come to deliver Jesus, but signs that Jews regularly expected to accompany the death of the righteous did follow Jesus' death (vv. 51-53). To both pagan and Jewish audiences these signs would indicate divine approval of Jesus and disapproval of his executioners (see Kee 1983:189; Best 1965:98; R. Brown 1994:1113-14). The raising of dead persons at Jesus' death (vv. 52-53) reminds us that by refusing to save himself, Jesus did save others (v. 42). Yet by mentioning only many of the saints, Matthew clearly intends this sign merely to prefigure the final resurrection, proleptically signified in Jesus' death and resurrection (Cullmann 1956a:168). Popular folk religion venerated the tombs of saints (Meyers and Strange 1981:162), and the very people who sought Jesus' death built those tombs (23:29-32); but Jesus, the holiest saint of all, had power to raise them."
Hope this helps,
Best wishes,
Snowrose