Yitzchak, the long-promised son of Avraham and Sarah, has a seemingly unflattering name. Instead of being named after some divine virtue, his name simply means "Laughed" commemorating the response of Avraham and Sarah when they were told by G-d that they would have a son at such an advanced age.
When Avraham is told by G-d that he will have a son, he laughs inwardly, and asks G-d only that Yishmael should repent and turn righteous. When Sarah is informed by an angel, she laughs at the idea of having a child at such an age.
Why then give their miracle child a name commemorating their skepticism?
Choosing the name, Sarah says, "Tzhok Natan Li Elohim", G-d gave me laughter, which here means joy. G-d gave Sarah reason to rejoice, her initial skeptical laugh of unbelief becoming a laugh of joy at the impossible. "And everyone who hears of it, will rejoice for me."
We laugh naturally at things that are ridiculous. We laugh because they are outside the norm. To Avraham and Sarah the idea of having a child at such an advanced age was ridiculous. But when it actually took place, then the skeptical laugh at the impossibility of such a thing because a joyful laugh at the possibility of it.
Avraham and Sarah did not doubt G-d. If they had been asked whether G-d could do such a thing, they would have agreed that He could. But were they willing to believe that it could happen to them?
Most religious people when asked would agree that G-d could create or destroy worlds. But can he take us out of a difficult trouble that we have? That we tend to be more skeptical about. Unconsciously they place limitations on G-d. The first laugh was the laugh of that limitation. The second laugh was the joyful laugh of seeing that limitation fall away.
In the Torah when people mock G-d, He then mocks them. How do people mock G-d, they assume that He is helpless to stop their evil. And how does G-d mock them? By showing them that He can. The "joke" is then on them.
The joke of Yitzchak was a beneficial joke. It was a punchline of faith. The punchline of a joke changes how we look at what came before it. It twists around our expectations. Similarly the punchline of Yitzchak showed Avraham and Sarah that their expectations of G-d had been limited and the culmination of their lives showed them another level of transcending that by seeing the infinite goodness of G-d.
Human faith is naturally limited. It is a ladder and there are always new rungs to climb. The birth of Yitzchak joyfully introduced Avraham and Sarah to a new level of faith.
The prophecy of Yitzchak showed that G-d could take the future of the Jewish people and bring it out of a child to a deeply elderly man and woman. The sacrifice of Yitzchak showed that G-d could take their child back from the edge of death. And that took even greater faith for Avraham. Finally with Yosef, Yaakov genuinely believed that his son was dead, from the testimony of his own children, and nevertheless G-d restored Yosef as well.
At each of these points there was a moment of transcendent joy at the realization that an impossible salvation has occurred. And through that joy, they and we, can learn to exceed ourselves in faith. When we move from skeptical laughter to joyful laughter, then we realize that the joke has always been on us and we laugh at ourselves with a new awareness of what we now know about G-d.