In order to attain to the perfect love of God it is necessary, moreover, to deny oneself by gladly embracing what is opposed to self-love, and refusing oneself what self-love demands. One day when St. Teresa was sick, they brought her a very palatable dish; the Saint would not touch it. The attendant urged her to eat, saying that the dish was well-prepared. "That's just the reason I abstain from eating it," replied the Saint. And so with us; what pleases us most, in that we must deny ourselves, and just because it pleases us. For example, we must turn our eyes away from this or that object because it is most agreeable to us; do a service to an ungrateful person just because he is ungrateful; take a bitter medicine just because it is bitter. According to St. Francis de Sals, our self-love ants to have a share in everything even in things the most holy. For this very reason, says the Saint, we must love even virtue without attachment. For example, it is necessary to love prayer and solitude; but when obedience or charity prevent us from devoting ourselves to prayer and solitude we should not be disquieted, but accept resignedly everything that happens by the will of God to thwart our inclinations.
The 12 Steps to Holiness and Salvation by St. Alphonsus Liguori