This is part of a longer quote by Mother Teresa:
Joy is prayer;
joy is strength;
joy is love;
joy is a net of love by which you can catch souls.
I love the picture that paints in my mind. Joyful people are so attractive. I don't mean necessarily physically attractive. People are naturally attracted to those who exude joy. I'm sure you can think of someone like that. Don't you always enjoy your time around those joyful people?