A mashal is told of a person who returned to a wedding hall to pick up something he had forgotten there. All the guests had already left, and he found the hall in a big mess. He remembers how everything was so beautiful just a few hours before, but now many of the tables were overturned, and those still standing had leftover chicken bones on them. The man thought, "If this is the end of a wedding, what is the whole purpose?" But then he remembered that a kiddushin happened. The chasan gave a ring to the kallah and said לי מקודשת את הרי. For this, the entire wedding was worthwhile.
But if the chasunah didn't occur, indeed he can ask, "What is the purpose of it all?"
The nimshal is a person’s life. We live seventy, eighty, ninety, or more years. Many things happened during this time, but then it ends, and the person is placed in the ground. Nothing remains but some bones. If, during his lifetime, there was kiddushin, which means he sanctified himself by performing good deeds, it was all worthwhile. But if there was no kiddushin, one can indeed ask what was the purpose of it all?
This can be hinted in the Chazal (Eiruvin 54.) דמיא הילולא כבי עלמא האי, "This world is like a chasunah." If you perform your mission, everything is worthwhile, otherwise, it is a waste, r'l.
The Divrei Shmuel said that this is the meaning of the pasuk יתרו וישמע, which means Yisro understood. He understood that he was superfluous in the world, with no purpose. He thought, "Was I brought to the world just to eat and enjoy pleasures? If I don't fulfill the mission that Hashem sent me to do in this world, I am extra."
I heard the following story:
As it is known, the mashpiah, Reb Mendel Futerfas zt'l, was sent to Siberia as a prisoner of the Russian government. Someone came to him one day and said, "Please, give me a brachah for success because tonight I will attempt to escape from here."
Reb Mendel looked at him as if he had gone mad. "How can you escape? There are walls all around us, guards standing on high towers watching, and wild dogs trained to attack anyone who escapes."
The man replied that he discovered a short moment every night when one guard left his post, and the next one came to take his place. For many days, during this moment, he approached one of the walls and drilled a drop in the wall. "Tonight, I have a drop more drilling to do and I will have created myself an escape door."
Reb Mendel gave him his brachos.
That night, Reb Mendel stood outdoors to witness what would occur. He saw the man approach the wall, drill, and kick the door he created with his foot. Part of the wall broke off, and he snuck through and ran to freedom. The dogs pursued him, but he was prepared for them. He dropped some pieces of meat from his pockets, and the dogs became busy with the meat and forgot about him.
The guard was watching from above. When he saw the dogs chasing after the prisoner, he was pleased and watched with satisfaction. The dogs were doing what they were trained to do. But when he noticed the dogs eating the meat the prisoner dropped for them, he became furious, grabbed his gun, and shot the dogs dead.
Sometime later, Reb Mendel was talking to this guard and asked him a question that had bothered him since that episode. "Why did you kill your dogs? What did the dogs do wrong, and besides, don’t you need your dogs?"
The guard replied, "Much money and effort was invested to train the dogs. If the dogs don't do their mission after all this, why do I need them? What purpose are they serving?"