The Messianic Signs
The key to this pericope is seeing Jesus' direct ties to the grounded promises of the Messiah. Jesus is not some obscure or novel happening of God, but infact is rooted in time, and relationship.
Elijah & John the Baptist
5 “Behold, I will send you Elijah the prophet before the great and awesome day of the LORD comes.
6:15 Ἠλίας, “Elijah”: It should be observed how Elijah appears in the same context as John the Baptizer (see the parallel in 8:28, as well as 9:13; cf. 1:6). Even more important is the association of Jesus with this collocation of Elijah and John the Baptizer—it is a question about Jesus, after all. See also 8:27–28 and especially 9:11–13. This strengthens the connections between the death of John the Baptizer and the ministry and mission of Jesus. Along with a reference to “a prophet like one of the prophets” (6:15), the reference to Elijah (see Mal 3:23 [ET 4:5]) solidifies the identity of Jesus as, among many other things, a prophetic figure (see the commentary on 1:2; see also 6:4 and the commentary on 6:34).
6:17 γάρ, “for/you know”: This conjunction gives the reason for Herod Antipas’ statement and introduces the next thirteen verses as a flashback (see the second textual note on 6:17).
6:18–19 John the Baptizer is similar to OT prophets who rebuked kings; see, e.g., Nathan rebuking David (2 Sam 12:1–15) and Elijah rebuking Ahab (1 Ki 17:1; 18:1–19; 21:17–24). Moreover, Herodias plays a role similar to Queen Jezebel, who, in the Elijah narrative, condemns God’s prophet (1 Ki 19:1–3).