These two axioms are the elementary Biblical themes, that even a simple reading will confirm. It is strange that the same term for which Sarah was reprimanded would now become her son's name. But the very fact that the same word serves two diverse meanings gives us pause. And being that this became Isaac's name, it means that the life of Isaac is somehow tied up in tzchok . The Torah tells us that Ishmael was a negative influence on Isaac.
Laughter is a basic human expression, on par with crying and screaming.
Crying is the reaction to sorrow and loss. A scream is the reaction to a threat. But laughter is a much more complex and deeper expression. It is the reaction of humans when the confines of reason have been broken. Thus, a person is certain that in a given situation there is no hope left.