Frequently, around our dinner table, when one of my kids takes a strong liking to some particular dish that has been served up, they will announce, "Hey, if any of you have any leftovers, I'll take them."
And usually, it happens just like that. IF one of the other kids has leftovers, they MIGHT remember to offer them to the one that said that before they throw their leftovers away.
Very occasionally (and I mean very) something else happens. One of my kids will respond to their sibling by offering some of their portion FIRST, before they themselves even take a bite! I'm not talking about them taking a much appreciated opportunity to get rid of something they don't like, I'm talking about a sacrifice of a portion of something they like a lot just for the joy of sacrificing it for their sibling.
Like I said, it's rare.
While my "receiving kid" doesn't usually seem to care whether they are getting the first fruit offering or the leftover, so long as they get more, God does care.
God does not want your leftovers. In any arena. He doesn't want your leftover time, money, energy, or life. He wants to be your highest priority, your first thought, your most important Person and Thing ever.
After what He's done for us, that is exactly what He is. And if we have seasons where that gets lost on us, then our lives are diluted and God must send someone like Malachi to wake us up.