Martin Luther wrote those words to remind us that love is more than self-serving; it is serving. A selfless act of giving is the pure essence of love which leads to the emotional joy we seek from selfishness.
I have friends who don't believe in God, but do great things for others for no other reason than it feels like the right thing to do. I would argue that is the God's cosmic power at work. God does not rely on seeking love for its own good but "the love of God flows forth and bestows good."
God gives love freely and in turn we, in the likeness of God, are called give freely. It could be money, a smile, a complement, a meal, time, a helping hand, ect. Whatever or however you serve, do so knowing, or not, that the love of God pours forth through you.