"Generous persons will prosper; those who refresh others will themselves be refreshed." (Proverbs 11:25, CEB)
No, it's not math, and it's not a financial statement, and it's not the Prosperity Gospel. The author of the Proverb is reminding us that giving to God's work on earth is a spiritual discipline, something that is held sacred between the giver and God. It's a reminder to us that we are invited to trust in God, and giving to God out of the first fruits of our labor is both an indication of that trust, and a freeing moment, in which we can go deeper into that trust.