Commentary for Leviticus 18:28

ולא תקיא הארץ אתכם THAT THE LAND VOMIT NOT YOU OUT — A parable! This may be compared to the case of a prince (i. e. a sensitive, refined person) to whom one gives a disgusting thing to eat which he cannot retain on his stomach but vomits it out thus Eretz-Yisrael is unable to retain sinners on its soil (Sifra, Kedoshim, Chapter 12 14). The Targum renders it by: ולא תרוקן a term for ״emptying out״ — it (the earth) empties itself of them.

ולא תקיא הארץ...כאשר קאה את הגוי, and by abstaining from these abominations the land will not spit you out eventually (for other sins) in the same absolute manner in which the people presently in that land are being disgorged by it.

ולא תקיא הארץ אתכם…כאשו קאה, "so that the land will not spew you out as it spewed out, etc." The Torah was not content with the statement in verse 25 that the land had already spewed out its inhabitants on account of their sins. It stresses the urgency of the matter much as what has been described in Torat Kohanim about the patient who receives a visit from a doctor who warns him not to eat certain things. This is followed by another doctor who warns the same patient that if he fails to heed his warning he would die just as another patient who had failed to heed the warning had died already. The patient takes the second warning more seriously than the first warning. Our verse may be viewed as the second warning.