So I comforted and kissed him in his dark Bedroom, but my comfort was not enough. (4-5)
Here the speaker tries to calm his son down, but he's just plain bad at it. As a father, it seems like he should be able to comfort his son, but, as he says, his "comfort was not enough." Good thing his wife is there to do a little crowd control.
[…] It's hardFor fathers to compete with mothers' love. (7-8)
Sounds sort of petty, dude. Maybe you should get over it? And since when is love a competition? This isn't The Bachelor, thank you very much. Still, in these lines the speaker's honesty about his feelings, coupled with the narrative drama of his crying child, opens up some of the complexity of love within marriage and parenting.
How can a father resent his son and his son's love? (14)
Who gets jealous of a baby? Aren't they all cuteness and giggles? But this question shows that our speaker is as baffled by the experience as the reader may be, and it's this question that leads him to a better understanding of his role as a father.