Many men turn aside from religion when their interest would be compromised. If I see two men walking together I cannot tell who is the master of the dog that is behind, but I shall discover directly. One of them will turn to the right and the other to the left—now I shall know who is the master of the dog, for when it comes to the turning point the dog will go with its master and leave the stranger. You cannot always tell whether it is God or Mammon that a man is serving when virtue is profitable—but when it comes to the turning point and the man has to be a loser for Christ in what he gives up for Christ’s sake—then sincerity is tried! Turning points are places where we may judge ourselves, for they are the only true criteria of our real character.
— Charles Spurgeon, Sermons (1866), p. 134
You could go through your whole life walking behind two masters, never knowing whether you are following Christ or following some false treasure, because you have so confused the two as lord. This is why the spiritual practices that Jesus gives us in the beginning of chapter six are so crucial. What better way to cut yourself off from the hoarding spirit of Mammon than by generously giving it away to others? What better way to counter the lie of self-sufficiency and personal productivity than by spending time in prayer and contemplation? And what better way to deny the power that worldly pleasure has over you, whether food or sex or anything else, than be temporarily fasting from its provision? These practices are defensive in that they expose the tendencies in your heart and shield you against the temptations of worldly treasure. But they are offensive also, because they strengthen your resolve to pursue God himself, and find delight in him alone.