Even before they can speak full sentences, many Jewish toddlers know to put a hand over their eyes during the recitation of the Shema. It is the best known hand gesture in Jewish prayer.
According to tradition, Rabbi Yehudah Hanasi was the first to cover his eyes while saying Shema (Talmud Berachot 13b). The Shulchan Aruch codifies it as standard practice.
Shema, as our most intense prayer, requires the consciousness of God’s unity and the underlying unity of all existence. Covering our eyes helps us concentrate on this.
After the first line of Shema, we recite v’ahavta (“and you shall love the Lord your God”) with our eyes open. V’ahavta discusses acceptance of the commandments. It is as though we move from the simplicity of Shema to the complex reality of putting into words and action what it means to live in God’s world.