I don't think I do, either, but as few people seem to get in this forum I will offer these thoughts.
For Lines 1 and 2:
The writer sees God as infinite (= without any boundary or ending).
God is also seen as a loving spirit whose love is so great that it cannot be kept within God, even though God is infinite. So the question is asked (right at the start) 'what sort of love is this?'.
In Lines 3 and 4 I'm struggling, but I think the writer is answering his own question by suggesting that God is both infinite and finite and therefore mysterious and beyond understanding.