A Christian girl once told Charles Spurgeon, the legendary preacher, that she was about to marry a man who didn’t attend church and made no allegiance whatsoever to Jesus. As any preacher worth his salt would do, Spurgeon reminded her of the command from 2 Corinthians 6:14:
Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And what communion has light with darkness?
The girl, however, had another plan. She explained that once she was married to the young man she would lift him up spiritually. Spurgeon listened to what she was saying and then asked her to stand on a chair. The girl was puzzled by such an odd request, but she obliged anyway. Once she was standing in the chair, Spurgeon said to her, “Now you try to pull me up to your level.” She tugged hard on the portly preacher, but no matter how hard she pulled she couldn’t pull him up on the chair with her.
Now it was Spurgeon’s turn. He said, “Now I am going to pull you down, and I want you to do your best to remain where you are.” Well, you can guess what happened. Despite the girl’s best efforts, Spurgeon easily pulled her down from that chair. Then he said to her, “That is what will happen if you marry that man. You won’t lift him up, but he will pull you down.”
Whether the unequal yoke is a marriage, some other type of personal relationship, or a business partnership, it is never God’s will for the Christian. As for illustrating the reason why, I’ve never read anything better than Spurgeon’s demonstration to that young girl. Over the course of time in the yoke, as the two different “animals” (to stick with the word-picture) pull the plow and do the work, the great differences between the Christian and the lost person will eventually become evident. The opinions will be contrasting. The standards of morality will be different. The specifics of conduct will be incompatible. And it will be through these differences that the Christian will, at least to some degree, get pulled down to the level of the lost person.