The speaker describes themselves as huge, and the two comparisons they choose are telling. A declaration of war and a laugh in church are both loud, disruptive and impossible to ignore. They are also a little dangerous or embarrassing, the kind of thing that makes a room go quiet. So the "big love" of the title seems to be less about a gentle feeling than about something overwhelming.
Then the poem turns on "but you." The speaker addresses someone who "must have somebody" and so can't give everything to one person. The final lines are the most interesting: the speaker is a "sum of others," as if they carry many people, or many selves, inside them. Asking the other person to care for that whole crowd is a big request. The mood is part confident, part vulnerable. The speaker boasts about their size, yet underneath there is a quiet plea: love all of me, even the parts that come with a lot of baggage.