This is less a request for an answer than Jesus voicing a deep desire. Barnes reads it, "And what would I, but that it were kindled," and explains that since the gospel could not be established without conflict, Jesus was "willing, nay, desirous that they should come." Gill puts it the same way: "what shall I wish and pray for?" and answers, "O that it were already kindled." The question shows Jesus eager for His mission to move forward, even knowing what it would cost.

Jesus goes on at once to speak of His baptism: "But I have a baptism to be baptized with; and how am I straitened till it be accomplished!" (Luke 12:50). Matthew Henry calls this "a baptism to be baptized with, far different from that of water and the Holy Spirit," the suffering Christ had to pass through. Then Jesus explains the fire's effect: "Suppose ye that I am come to give peace on earth? I tell you, Nay; but rather division" (Luke 12:51).

The Greek reads, word for word, "and what do I wish, if already it was kindled." Because it can be read as a wish, the ESV translates it as an exclamation: "would that it were already kindled!" The KJV keeps the question form.

Commentators read the "fire" differently. Barnes says, "Fire, here, is the emblem of discord and contention," the result of men's opposition to the truth. Gill offers several possibilities: the gospel itself, "which is as fire, that gives both light and heat," persecution for the gospel's sake (the reading he prefers, "or rather"), or the coming of the Holy Spirit "in cloven tongues, like as of fire." Barnes ties the fire directly to the division Jesus describes next (Luke 12:51-53).

Here we glimpse the heart of Jesus toward His mission. He is not reluctant. He longs for the fire to be kindled, and He feels pressure ("how am I straitened") until His baptism of suffering is "accomplished" (Luke 12:50). The One who calls His servants to readiness (Luke 12:40) is Himself fully committed to His own mission.

The fire is costly. Matthew Henry notes that Christ's religion is "pure, peaceable, and loving," yet it causes conflict because it is "contrary to men's pride and lusts." Jesus does not hide that cost. He names it plainly and goes forward anyway.