You shall love the LORD your God with all your heart and with all your soul and with all your might. (Deuteronomy 6:5)
The literal commandment is that we should love G-d with all our heart, soul, and might.
Messiah affirmed this commandment when He was asked "what is the greatest commandment":
Jesus answered, "The foremost is, 'HEAR, O ISRAEL! THE LORD OUR GOD IS ONE LORD; AND YOU SHALL LOVE THE LORD YOUR GOD WITH ALL YOUR HEART, AND WITH ALL YOUR SOUL, AND WITH ALL YOUR MIND, AND WITH ALL YOUR STRENGTH.' (Mark 12:29-30)
The New American Standard Bible (NASB) translates this passage in all capitals to reflect that it is quoting from Deuteronomy.
To discover more regarding what Scripture says about "The Greatest Commandment" see this article from Psalm11918.org.
This commandment shows us the absolute love that Messiah had for His Heavenly Father and the absolute unity that comes from such a love (see John 14:23-24).
Messiah expressed the love we are commanded to have (with all His heart, all His soul, and all His might) by being obedient to the commandments (John 14:15, 15:10) even to the point of death on a stake (Philippians 2:8).
The traditional observance of this commandment is focused on obeying G-d's commandments out of a love and reverent fear as one might have for an earthly father. This is consistent with Messiah's observance as well since He kept the commandments and taught others to do the same (Matthew 28:19-20).
We are able to fulfill this commandment today and should love the LORD our God with all our heart and with all our soul and with all our might.
The Hebrew word translated as "love" is אהב [ahev] and it is a verb. In affirming this particular commandment as the greatest, Messiah called us to action. Love is an action verb. It is not an emotional state of emotion but instead it is the act of doing.