When you fill a car’s tank with gas, the results are predictable. That tank of gas will take you only so far. But when you fill someone’s tank with kindness, you never know how far it will go.

I was struck by that thought when reading a biography of the famous evangelist D. L. Moody, a native New Englander. Growing up in Northfield, MA, Moody lost his father when he was only four years old. His bereaved mother did the best she could for Moody and his seven siblings, but the family often struggled to have the necessities of life.

When he was a teenager, Moody moved to Boston to look for work. There he visited a Sunday school class, attended by students from Harvard College. On his first visit, when the teacher told the students to turn in their Bibles to the Gospel of John, Moody was given a Bible, but had no idea where to find the Gospel of John. As the awkward young Moody began fumbling through the pages, the cultured Harvard students began to point, whisper, and laugh.

The Sunday school teacher, Edward Kimball, came to the rescue. He handed Moody his own Bible, which was opened at the right place, and silenced the sneers with a stern glance. Moody never forgot that kindness, saying that he would “stick by the fellow who had stood by him, and had done him a turn like that.”

But another act of kindness from Kimball would have an even greater impact—not only on Moody’s life, but on the lives of untold thousands. One morning, Kimball walked to the shoe store where Moody worked. He had one mission: to urge Moody to put his trust in Jesus Christ as his Savior. “I went up to him and put my hand on his shoulder,” Kimball later recalled, “Then I made my plea.” He told Moody of Christ’s love for him, and there Moody “gave himself, and his life, to Christ.”

We have to wonder whether Moody would have paid any attention to Kimball if it had not been for that first act of kindness in his Sunday school class—keeping a bumbling country boy from being humiliated. Little could Kimball know that years later, that awkward teenage boy from Northfield, MA would become the most well-known evangelists of the 18th century.

As Christians, we find the source of kindness in the character of God himself. As Paul writes in Titus 3:4-5, “When the kindness and love of God our Savior appeared, he saved us, not because of righteous things we had done, but because of his mercy.” Even though the kindness we show to others is just a faint imitation of God’s kindness toward us, it can still have a tremendous impact.

Let us be kind to one another. We never know how far one act of kindness can go.