Wonderful quotes about giving from C.S. Lewis, the best Christian apologist of the 20th Century. I found these very challenging.
Charity–Giving to the poor–is an essential part of Christian morality…I do not believe one can settle how much we ought to give. I am afraid the only safe rule is to give more than we can spare. In other words, if our expenditure on comforts, luxuries, amusements, etc., is up to the standard common among those with the same income as our own, we are probably giving away too little. If our charities do not at all pinch or hamper us, I should say they are too small. There ought to be things we should like to do and cannot do because our charitable expenditure excludes them. Mere Christianity, bk. III, chap. 3, para. 7, pp. 81-82
The limit of giving is to be the limit of our ability to give. English Literature in the Sixteenth Century, Introduction, para. 53, p. 35