Sfas Emes on VaYeira

The Sfas Emes asks why Yitzchak's name is so similar to the word Metzachek, which is used regarding the actions of Yishmael and explained by the Rabbis as referring to spilling blood, idol worship and forbidden relations. The Rebbe explains that evil people think that they are happy because they give into their impulsive desires, but Yitzchak saw his Evil Inclination as a joke of sorts and realized that he didn't have to take it so seriously. Although Yitzchak was the manifestation of complete awe of God/Midat Hayirah, his face always exuded joy because he realized that the only thing to fear in this world was God and God alone. While Yishmael might have thought he was happy because he was able to indulge in physical pleasure, the joyous face of Yitzhcak was a continence of true eternal bliss.