Alma’s prayer has two parts. These five verses are the first part of the prayer, where Alma describes to God the visible and audible sins of the Zoramites. The description of their sins is bracketed by Alma asking how long the Lord will suffer such wickedness to continue. We see that phrase in verse 26 and then later in verse 30.
In between, Alma reiterates the major problem that he sees with Zoramite worship: they are prideful, as manifest in their costly apparel. As in other uses of “costly apparel” in the Book of Mormon, it is a sign of apostasy. The problem is not so much the wealth that allows it, but rather that the costly apparel signals a visual distinction between those who have and those who have not, and that visual distinction leads to the presumption of a real distinction, where pride dictates that those who can have the costly apparel are therefore better than those who do not.
Of course, the Zoramite rejection of the coming Messiah is an important concern, and, therefore, Alma mentions it specifically in verse 29.