勸善之功 The Merit of Urging Goodness
正說處，早見直符使者捧定了道家文書、僧家關牒，到天門外傳遞。那符使見了行者，施禮道：「此意乃大聖勸善之功。」正说处，早见直符使者捧定了道家文书、僧家关牒，到天门外传递。那符使见了行者，施礼道：「此意乃大圣劝善之功。」
逐句解 Line by line
Just as they were speaking, up came the Duty Talisman Officer, bearing the Daoist documents and the Buddhist certificates in both hands, to hand them in at the Gate of Heaven.
直符使者 is the officer on duty for the day in Daoist ritual administration — a rota post, quite literally the messenger whose shift it is. 關牒 is an official certificate passed between offices. The prefect's paperwork from a few passages back has arrived, and it has arrived faster than Pilgrim did.
The talisman officer saw Pilgrim, saluted him and said, "This comes about through the Great Sage's merit in urging goodness."
勸善之功 — the merit of exhorting to goodness. It is the chapter's own title looking back at itself: the two lines of the title promised that the Great Sage would urge goodness and bestow rain, and here is a passing official saying the first half has been done.
The documents arrive, and a messenger stops to compliment Pilgrim on the merit of urging goodness.
It is worth pausing on that phrase, because it is lifted almost exactly from the chapter's own title. The novel is telling you, through a minor official with a delivery to make, that the thing the chapter set out to do has now been done — and there are still fifteen passages to go, all of them about the consequences.