Idolatry: Saints should not Covenant with Those Who Practise
Source: TTT
Exodus 34:12, 15
Be careful not to make a treaty with the inhabitants of the land you are entering, lest they become a snare in your midst. / Do not make a covenant with the inhabitants of the land, for when they prostitute themselves to their gods and sacrifice to them, they will invite you, and you will eat their sacrifices.
Deuteronomy 7:2
and when the LORD your God has delivered them over to you to defeat them, then you must devote them to complete destruction. Make no treaty with them and show them no mercy.