Hear, O Israel: The Lord our God is one Lord.
It’s taken for granted today that there is only one God. Though, now that civilization has cut it mooring to Judeo-Christian theology, there’s no particular reason why that should go on being the case. Where our ancestors believed in one God as a matter of reason and revelation, we believe in one God as a matter of custom and unthinking cultural inertia. It will not be any surprise at all when some popular movement arises to try to revive polytheism just as popular movements have already tried to promote atheism. When such movement arise, the Church will go on saying what God’s people have been saying since the time of Moses: The Lord is one. Polytheism is really just an attempt to chop a lot of little godlets out of the one true God. It takes this or that favorite aspect of the divine nature and pretends that’s all there is to God. Falsehood and false gods nearly always are born when a truth gets ripped out of the whole Truth and taken in isolation.