The devil would convince us that we don't have time to do the things we need to do if we take time for God. He will say, "If you pay your tithe, you won't have the money to pay the bill coming due next week." This is a lie all the way through.
Everybody thinks that when you mention "tithe", you are just talking about their money. God wants 10% of you. He wants 10% of your time. He owns you anyway. The word "tithe" means 10%. So we're not talking just about money.
You have a free will, so you can say, "No, I'm not going to give God anything." OK, then you will reap the blessing of that ... which is nothing. You get back what you give.
2 Corinthians 9:6,7 AMP. ... Remember this: he who sows (gives) sparingly and grudgingly will also reap sparingly and grudgingly, and he who sows generously and so that blessings may come to someone, will also reap generously and with blessings. Let each one [give] as he has made up his own mind and purposed in his heart ... not reluctantly or sorrowfully or under compulsion, for God loves (that is, He takes pleasure in, prizes above other things, and is unwilling to abandon or to do without) a cheerful (joyous, prompt-to-do-it) giver ... whose heart is in his giving.
Reverend Robert W. & Mary C. Butler