The point of the verse may be to prohibit swearing because on the Temple is swearing on the Divine. This message was said more directly in Matthew 5:33, and the following verse, Matthew 23:22, echoes Matthew 5:34.
This verse again repeats another of the couplets of this section. This is the style of Jesus's humor in repetition, creating an expectation that the pattern will be followed but then breaking it. The expectation created by the previous verses is that this one would end with "everything in it" or words to that effect, but instead, it ends with "the one occupying" in it.
The word translated as "dwelleth" and "dwells" is not the word usually translated as "dwell" in the NT. Instead, it is a rare word that works more like our "occupy" or "inhabit," taking a direct object. It is a verb in the form of an adjective, "occupying," preceded by an article, completing the idea of a noun, "the one occupying it."