God has attached his blessing to a percentage (10 %) – or the tithe.  Why?  There may be more interesting reasons, but in short – We give 10% because God told us to.   If he left it up to us to decide how much to give we would probably pick a much lower percentage.   We would pick that lower percentage until we figured out someone gave more; then, our pride would want us to beat the other giver!    Competitive giving produces wrong motives.   Our stinginess and pride keeps us from giving with pure hearts.   Therefore, God established a specific percentage to test our obedience.   Everything we own is his, yet he asks for 10% from us as a test of obedience.