He has scattered abroad his gifts to the poor.
2 Corinthians 9:9 NIV
It's one thing to give because it puts God on your side financially, but there's an even greater reason: "He has scattered abroad His gifts to the poor; His righteousness endures forever." At first glance you may think, "What's that got to do with anything?" A lot! God's committed to healing the hurts of our world; that's why He speaks of "gifts to the poor."
When we get involved with God through our giving, we're taking our place in a plan that's bigger than our own interests - or our tiny bag of seed. We're participating in His plan to reach the world. God's concerned about the poor, and about sharing with every person on earth the good news of the Gospel. Those are His objectives and He's committed to them. And they're going to cost money. A lot of it! Now the truth is, God will get the money from somewhere, but He'd like to partner with you to accomplish it.
You say, "But I'm afraid if I give more I won't have enough to meet my own needs!" Think about what you just said. Why would God drain you of your resources, then not replenish them to accomplish through you what He's committed to doing? That doesn't make sense. If you're a partner with God why would He hinder your ability to give toward the things that matter most to Him: the needy, and winning a lost world?
The truth is, God's going to do it with or without you. He's just giving you an opportunity to get involved with Him. Don't miss out on it!