I remember an incident from high school many years ago. We had an assignment due on Monday and on Saturday night it snowed... and snowed and snowed some more! Needless to say, there was no school on Monday. Actually, there was no school that whole next week.
We returned to school the following Monday and only 3 students out of 28 turned in their assignments. The rest of us begged and pleaded for more time and, sighting the heavy snow and subsequent power outages, our teacher extended the deadline one more day. The next day, 12 kids handed in their assignments. The other 13 students gave numerous lame excuses and, to our amazement, the deadline was extended yet again. The next day 4 more students handed in their assignments and I couldn't believe the 9 others could be so bold as to ask for another extension! To make a long story short, the last student handed in their assignment the following Monday... two whole weeks late!
When our assignments were graded and handed back to us, our grades were horrible! The teacher didn't take off points for the papers being late, but he went through each of them with a fine tooth comb! He marked off for every little minor mistake. He marked things that he normally let go. Naturally, we cried foul. Why was he being so mean? Why was he being so picky? Why was he trying to fail us all? Why? Why? Why?
Finally, someone made the fatal mistake of saying that we didn't deserve such poor grades. The teacher asked if we all felt the same way and we all did. He asked us to hand the papers back and he would re-grade them and this time, he would give us the grades we deserved. He then proceeded to do just that.... we got zeros! All but the 3 students who turned their work in on time got zeros! And we deserved them. We took advantage of our teacher's mercy and then complained when he graded our papers very strictly.
God has let time go on for better than 2000 years now, his mercy giving all of us time to repent and turn to him. We seem to think that, because he has let us go so long, either he doesn't care how we act or maybe he doesn't even exist! My guess is that there will be a lot of whining and complaining on judgment day when we stand before him to give account for our lives. I bet the complaints of "this is unfair" and "you're unjust" get used a lot. I bet a bunch of folks will say "we don't deserve this!" when they're sent to eternal punishment.
We have abused God's mercy and grace and used his patience as an excuse to sin against him. But not much longer.