They saw only a lonely foreigner in need of a welcome, a person in need of clothing, someone sick or in prison who needed come company. Doing things for God was the last thing on their minds. They were only doing what needed to be done. That's how faith in Christ works. It does what needs to be done even before the Law tells you what to do.
Faith does what comes naturally.
It's like an apple tree producing apples. Or a tomato plant making tomatoes. Faith gives food to the hungry, drink to the thirsty, clothing to the naked, welcome to the stranger, company to the sick and imprisoned, without being told, without thinking about it. That's how faith in Christ serves Christ. The One who fasted for us in the wilderness, who felt the pangs of our hunger, is hidden in the hungry.