Today someone asked me to explain why I cover my eyes for about two minutes while reciting the Shema prayer. I responded that it's to concentrate.
Then he wanted to know what takes a whole two minutes. So I explained that I spend the time reviewing two books; "The Gate of Unity" by Rabbi Bachya ibn Pequda and "The Gate of Unity and Faith" by Rabbi Shneur Zalman of Liadi. The former teaches monotheism, that the Creator is One. The latter teaches monism, that He is All.
Then I concluded, "Don't you agree that it takes at least two minutes to review two books?"