Luther from his House Postils (from Pastor Weedon):
"To sum it all up: we will be good Christians, first of all, when we have a firm faith and trust in God's goodness; second, when we are grateful to God and our fellowmen; and third, when we patiently tolerate ingratitude as we keep on doing good to all people.
In any case, nine people will be ungrateful for every one who is grateful and thanks you for a good deed. And it may well be that the one who thanks you and is grateful is the one of whom you least expected it, just like this Samaritan. May our loving Lord God grant his grace that we remember this and keep growing in our sanctification. Amen."