That explanation doesn't require theology. I've seen Peter Singer make the case that it's only "true altruism" if you're just as happy when someone else does something good as when you do so yourself.
Sort of, but the difference is that Christian altruism results in an increasing expectation of being praised and rewarded by God on the other side for being his agent of love to others in this life.
The result is a lot of joy, knowing one has brought blessing and joy both to God and to other people.
The result is a lot of joy, knowing one has brought blessing and joy both to God and to other people.