Genesis 17:19

Indeed. — In the Hebrew this word comes first, and is intended to remove all doubt or desire for any other turn of affairs. It should be rendered, “And God said, For a certainty Sarah thy wife shall bear thee a son.”

Thou shalt call his name Isaac. — That is, he laughs. The name was to be a perpetual memorial that Isaac’s birth was naturally such an impossibility as to excite ridicule.