Nun and Prostitute Comparison

Alright, listen up, you big dummy. This joke is playing on the word "father" and also, well, the... *activities* of a prostitute. A nun, she's all about God, right? So when she says "God is my father," she means it in a spiritual, devoted way. Now, the prostitute, she's got a lot of... *business* partners. So when she says "Who's the father and who is my son?" it means she's slept with so many guys she wouldn't know who the dad of a kid might be, and also, ew, she might be sleeping with guys who could be her actual sons without knowing. It's a crude joke, you blockhead, but that's where the twisted humor comes from. You got it now, or do I need to draw you a picture with crayons?