I just read about this great illustration Corrie ten Boom used to teach "how God would repay the generous."
She stood in front of the class of young missionaries-in-training and placed two bottles before them, each filled with sand. One had a narrow mouth and the other had a wide mouth. She picked up and poured from the wide-mouthed jar. The sand quickly poured out onto the table, leaving the jar empty. The then started pouring sand from the narrow-mouthed bottle. The sand trickled out, taking a long time to empty.
“You see students,” she said, waiting for the thin line of sand, “this bottle is like some Christians. They give to God, but not so quickly and freely. But look what happens.” She finished and began to reverse the process, pouring sand back into each bottle. The wide-mouthed jar was quickly filled, spilling excess over the top. However, it took her a long time to painstakingly refill the narrow-mouthed jar with sand. It had given slowly and now it received just as slowly.
Which bottle are you like?
Cunningham, L. (1991). Daring to Live on the Edge: The Adventure of Faith and Finances. Seattle: YWAM. (p. 81)