Shema is the first prayer that a child learns and the last that a Jew says before he dies. The mitzvah is to say it twice, morning and evening every day, in between. Shema encompasses the most fundamental beliefs of Judaism. The first paragraph speaks of God's unity, loving God, learning Torah and passing on Judaism to our children; the second discusses reward for good actions, and the opposite for bad ones and the third is about remembering the Exodus from Egypt and the mitzvah of tzitzit.
So many world-shaking ideas in a few lines; let us briefly look at one, loving God. The Shema bids us to love God with all our heart, soul and might. Can love of anyone or anything be commanded? Maimomides answered that the command is to meditate on the amazing glory and wonder of the created world, principally through studying science, and so to come to love and awe of the One who made it. Rav Shneur Zalman of Liadi, founder of Lubavitch, gave another answer. Fulfilling the command to love God is a consequence of reflecting deeply on the previous verse, Shema Yisrael… the declaration of God's unity. From perceiving God's unifying presence behind the confusion and contradictions of the world, love will spring.