"for she (a returned divorcée) is an abomination before the L-rd": As it is written (Jeremiah 3:1) "If a man divorces his wife, and she goes and marries another man, can he return to her again?"
"for she is an abomination": R. Yehudah said: She is an abomination, but her child (of the renewed union) is not an abomination.
"And you shall not make sinful the land": Beth-din is hereby being exhorted (to insure that this does not happen).
(Devarim 24:5) "If a man take a new wife": This tells me only of a virgin. Whence do I derive (the same for) a widow and a divorcée? From (Ibid.) "and he shall rejoice his wife" — in any event. If so, why is it written "new"? One who is "new" to him — to exclude a returned divorcée.