Bede : And the Lord said to Abraham: "Sarah your wife shall bear you a son, and you shall call his name Isaac." Isaac is interpreted as Laughter, and it is not to be doubted that he was so called because when his birth was announced, Abraham laughed in his heart. This laughter fittingly signifies the joy of the New Testament, in which the children of the promise, with the Lord dwelling within them, shall rejoice forever. — Commentary on Genesis (Hexaemeron) Bede : For what follows: "And I will establish My covenant with him for an everlasting covenant, and with his seed after him," etc. He says his seed in those who, by imitating the faith of Abraham, merit to hear from the Lord: "Blessed are you who weep now, for you shall laugh" (Luke 6:21); to such as these the Apostle, joining himself, says: "Now we, brethren, as Isaac was, are children of promise" (Galatians 4:28). Specifically, however, the name Isaac, that is, laughter, which is born from the promise, fittingly applies to the Mediator between God and men, about whose birth an angel said to the shepherds: "Do not be afraid, for behold, I bring you good tidings of great joy which will be to all people" (Luke 2:10). — Commentary on Genesis (Hexaemeron)