* **And if you ** - The pronoun "you" refers to the people in the crowd.
* **this is Elijah ** - "This" refers to John the Baptist. This phrase is a metonym saying that John the Baptist corresponds to the prophecy of Elijah in the Old Testament, but it is not saying that John the Baptist is actually Elijah. (See: [[en:ta:vol2:translate:figs_metonymy]])