R. C. Sproul tells the story of when he was a college professor. At the start of the semester, the class of about 150 students had three papers due, let’s say, at noon on October 1st, November 1st, and December 1st. The penalty for a late paper was a zero grade. At noon on October 1st, 140 students strolled in and put their papers on his desk. Sproul asked the 10 students whose papers were late, “Where are your papers?” “Oh, Professor Sproul,” they pleaded, “we have had so much work, and we are having such a hard time adjusting to college. Please give us an extension.” “Okay,” said Dr. Sproul, “but the next time your papers are late, you will receive a zero grade. Agreed?” “Yes,” they all replied.
At noon on November 1st, 125 students strolled in and put their papers on his desk. Sproul asked the 25 students whose papers were late, “Where are your papers?” “Oh, Professor Sproul, we had mid-terms, and we just did not get time to write the papers. Please give us an extension.” “Okay,” said Dr. Sproul, “but this is your final warning. The next time your papers are late, you will receive a zero grade. Understand?” “Yes,” they all replied. At noon on December 1st, 100 students strolled in and put their papers on his desk. Sproul asked the 50 students whose papers were late, “Where are your papers?”
“Oh, Professor Sproul, don’t sweat it! Don’t worry about it! We’ll get the paper to you in a day or two!”
“Each of you will get a one letter grade reduction!” said Dr. Sproul. Enraged, the students shouted, “That’s not fair!” “Oh, you want me to be fair!” said Sproul, “I will be fair. I said that if your papers were not on my desk by noon today, you would receive a zero grade. Since they are not here, I will be fair and just, and you will receive a zero grade.”
What Sproul was illustrating is that as the professor setting the rules, he had the prerogative to extend mercy to who he wanted to extend mercy. He did so the first two times the papers were late, and that extension of mercy was not inconsistent. But then the students presumed upon Sproul’s mercy. They thought that there would be no penalties for their failure to perform according to the instructions. So, when they asked for justice (by saying “That’s not fair!”), they received the full penalty for their failure to perform. It is unthinkable that God could ever be unrighteous or unjust. Paul says strongly, “By no means! God could never be unfair or unjust.” He bases his argument on Exodus 33:19, where God says to Moses, “I will have mercy on whom I have mercy, and I will have compassion on whom I have compassion” (9:15). – Selected from a sermon entitled “IS God Unjust?” by Freddy Fritz (sermoncentral.com)