The point of the adverb is that Christ is moving things along to his ultimate appearing as quickly as he can, within the parameters of what God has ordained must happen in the New Testament dispensation (see the content of the scroll of Revelation 5:1–14). The Greek term used here is not so much a reference to time as to speed (so, quickly, swiftly, as soon as possible).
12 “Behold, I am coming soon, bringing my recompense with me, to repay each one for what he has done.