Even visions tarry. If what you have is too small to be your harvest, then it must be your seed for sowing. Moses only had a staff, but God used it. David only had a sling-shot, but God used it. The little boy only had a tuna fish sandwich for lunch but God was able to feed 5,000 with it.
Some seed is for eating and some is for sowing.
This point seems so obvious, yet I can't tell you the number of times I have observed people who have expected a harvest but never plant any seeds. We look for riches, but don't go to school. We want a word from God, but don't read our Bibles. The widow of Zarephath even gave her last seed. Tithing teaches us to give God our first fruits.