In commenting on this verse [Q3:142], al-Rāzī says,
Know that love of this world cannot coexist with happiness in the Hereafter, and to the degree that one of them increases the other diminishes. That is because happiness in the world only is achieved by the heart's occupation with worldliness, and happiness in the Hereafter can only be achieved by emptying the heart of all that is other than God and filling it with the love of God. Not all those who affirm the religion of God are truthful. Rather, in the difference there is a question of the sway of things that we hate and things that we love. Love is that which does not diminish with difficulty and does not increase through fulfillment. If love survives the onset of suffering, it is shown to be true love.SQ, p. 169.