# who comes after me

John is speaking about Jesus. The phrase "comes after me" means that John's ministry has already started and Jesus's ministry will start later.

# me, the strap of whose sandal I am not worthy to untie

Untying sandals was the work of a slave or servant. These words are a metaphor for the most unpleasant work of a servant. Alternate translation: "me, whom I am not worthy to serve in even the most unpleasant way" or "me. I am not even worthy to untie the strap of his sandal" (See: [[rc://en/ta/man/jit/figs-metaphor]])