The Gospel reading is from Mt 17:9a, 10-13. The first reading from Sirach (48:1-4, 9-11) prepares us for Jesus words by speaking of the great prophet Elijah. Undoubtedly, Jesus had this passage, and many other related passages, in mind when responding to the question from Peter, James, and John after they had just seen Jesus conversing with the prophet during the Transfiguration.

[T]he disciples asked Jesus,
“Why do the scribes say that Elijah must come first?”
He said in reply, “Elijah will indeed come and restore all things;
but I tell you that Elijah has already come,
and they did not recognize him but did to him whatever they pleased. (vv. 9a, 10-12)

“‘In popular belief and scribal teaching Elijah was expected to return in some sense in the last days and prepare the way for the Lord (Mal 3:23-23; Sir 48:10). Since Peter, James, and John just saw Elijah speaking with Jesus, they wonder if that expectation has now been fulfilled. Jesus agrees with the popular belief saying, ‘Elijah will indeed come and restore all things,’ a reference to Elijah’s ministry of preparing the people for the Lord by calling them to repentance and mending kingship relationships wounded by sin (Mal 3:23-24). However, Jesus adds the contrasting phrase, ‘but I tell you.’ As in 5;22, these words denote a contrast in which Christ offers something in addition to what was taught previously. While Jesus endorses the scribal expectation of Elijah’s return, he adds that ‘Elijah has already come.’ In other words, the scribes and many other is Israel were righto look for Elijah’s return but, unfortunately, they have missed his coming. The great eschatological reappearance of Elijah has already taken place in the person and ministry of John the Baptist (11:14; 17:13; see 3:4). Like Elijah, John was a great prophet who called the people to repentance and was persecuted by a wicked king (see 14:3-12).” (The Gospel of Matthew [Catholic Commentary on Sacred Scripture], 219-220)

The first thing to comes to mind here is John the Baptist directly addressing whether or not he was Elijah returned in John chapter 1. John denies it. But does Jesus affirm it here? The always helpful Catholic Answers addresses this seeming conundrum. Also check out the brilliant Dr. John Bergsma who grapples with this same question while expounding on different Mass readings (particularly starting at 4:23 but I recommend listening to it all for further context and deeper insights).

For a refresher on Elijah’s exciting story, read 1 Kgs 17-19, 21 and 2 Kgs 1-2.

(The Responsorial Psalm reminds me of the St. Louis Jesuits song based on it, Save Us, O Lord. These men get substantial flak for their music from certain corners, but I very much appreciate at least some of their work. This song is one of my favorites of theirs.)

God bless.