An intended purpose is what motivates an action. An outcome is what follows, whether or not the agent intended it.
Pharaoh's family took the child in, not to create an enemy, but the subsequent event became one of enmity and grief for them. Describing such an unintended but eventual result in the language of an end gives the sentence its striking rhetoric.
Incorrect: “Because the lām occurs, the household must have intended enmity.”
Correct: The particle has to be interpreted in light of context and the actual consequence.