The speaker is telling a would-be lover exactly what they will and won't accept. The message is blunt: if you're going to love me, do it fully, or don't do it at all. Half-hearted love, the kind that asks me to be grateful for what's there instead of what's missing, isn't enough. The line "I am not a reservoir" suggests the speaker refuses to be something that simply stores up whatever small amounts they're given.
The second stanza turns to what the speaker can't do. They won't walk on coals or leap into the tides on blind faith. The admission that their "box of excuses has reached its limit" sounds tired and honest, as if they've been cautious or hurt for a while and have run out of ways to put things off. The final two lines set the test: real love should shine even "on the darkest nights." The mood is guarded and firm, with a quiet vulnerability underneath, since someone who asks for this much clearly wants to be loved well.