Matthew 6:24

No man can serve--The word means to "belong wholly and be entirely under command to." two masters: for either he will hate the one, and love the other; or else he will hold to the one, and despise the other--Even if the two masters be of one character and have but one object, the servant must take law from one or the other: though he may do what is agreeable to both, he cannot, in the nature of the thing, be servant to more than one. Much less if, as in the present case, their interests are quite different, and even conflicting. In this case, if our affections be in the service of the one--if we "love the one"--we must of necessity "hate the other"; if we determine resolutely to "hold to the one," we must at the same time disregard, and (if he insist on his claims upon us) even "despise the other." Ye cannot serve God and mammon--The word "mamon"--better written with one m--is a foreign one, whose precise derivation cannot certainly be determined, though the most probable one gives it the sense of "what one trusts in." Here, there can be no doubt it is used for riches, considered as an idol master, or god of the heart. The service of this god and the true God together is here, with a kind of indignant curtness, pronounced impossible.

— Jamieson-Fausset-Brown Commentary (public domain)