There most likely is no more famous verse in the Old Testament among the ancient Israelites and probably even Jewish worshippers today than this passage from the book of Deuteronomy. And we learn that this commandment, from the lips of Jesus Christ, is the most important. That this is the most important commandment is nothing short of universal truth.
Hear, O Israel: The Lord our God, the Lord is one. Love the Lord your God with all your heart and with all your soul and with all your strength.
These commandments that I give you today are to be upon your hearts. Impress them on your children. Talk about them when you sit at home and when you walk along the road, when you lie down and when you get up. Tie them as symbols on your hands and bind them on your foreheads. Write them on the doorframes of your houses and on your gates.
When the Lord your God brings you into the land he swore to your fathers, to Abraham, Isaac and Jacob, to give you—a land with large, flourishing cities you did not build, houses filled with all kinds of good things you did not provide, wells you did not dig, and vineyards and olive groves you did not plant—then when you eat and are satisfied, be careful that you do not forget the Lord, who brought you out of Egypt, out of the land of slavery.
Fear the Lord your God, serve him only and take your oaths in his name.
New International Version, 1984 Edition