1 Thessalonians 2:1-2
For yourselves, brothers, know our entrance in to you, that it was not in vain:…
A young man was engaged in teaching a class of rather wild lads in a Sabbath school: He thought that he was not qualified to make any impression upon them, and got much discouraged. By the inducements of his fellow teachers and superintendent, he was prevailed upon to keep at the work for years, till at last he absolutely refused to continue it longer. Many years afterward an eminent missionary wrote home: "Is that gentleman who taught in the Sabbath school still living? If he is, please let him know that there is at least one living who dates his conversion to Christ from the lessons received in his class." So you see that, although the teacher gave up his work because he saw no fruit, yet the seed sown was not lost; one soul, if not more, was saved, and used as God's means for saving many others.
Parallel VersesKJV: For yourselves, brethren, know our entrance in unto you, that it was not in vain: