en_tn_condensed/luk/12/50.md

I have a baptism to be baptized with

Here "baptism" refers to what Jesus must suffer. Just as water covers a person during baptism, suffering will overwhelm Jesus. Alternate translation: "I must go through a baptism of terrible suffering" or "I must be overwhelmed by suffering as a person being baptized is covered by water" (See: rc://en/ta/man/jit/figs-metaphor and rc://en/ta/man/jit/figs-activepassive)

But

The word "but" is used to show that he cannot cast the fire on the earth until after he goes through his baptism.

how I am distressed until it is completed

This exclamation emphasizes how distressed he was. Alternate translation: "I am terribly distressed and will be so until I complete this baptism of suffering" (See: rc://en/ta/man/jit/figs-exclamations)