"The first is: Hear, Israel! The Lord, our God, is One Lord; and you shall love the Lord, your God, with all your heart, with all your soul, with all your mind and with all your strength." (Mark 12:29-30)
*From Christian Community Bible (Catholic Pastoral Edition):
You shall love the Lord, your God. This first commandment is not among the Ten Commandments of Moses, which only speak of "serving God." We do read it in Deuteronomy 6:4.
To love God is not a commandment like others, because the commandments show specific actions that should be undertaken or avoided, i.e., you shall rest on the day of the Lord, or you shall not commit adultery, On the other hand, when it comes to loving God there is no limit.
The commandments of the Bible (especially the Ten Commandments of Moses) merely express in a clear manner the demands of our conscience. It should not be necessary to tell us not to steal, and not to slander others. Nevertheless, it is necessary to teach this to children and to unscrupulous persons. Paul says, "The Law was not intended for the good, but for those who do evil" (1 Timothy 1:9).
It is the reason why the love of God is not presented in the New Testament as a commandment, but as the fruit of the Spirit that God gives to His sons and daughters: Romans 8, 15 and 22. God is the first to be loved (Matthew 6:9-10, 1 John 4:17) most especially in the person of His Son: 2 Corinthians 5:16, 1 Peter 1:8. There is no authentic love of neighbor without the love of God: 1 John 5:2.
You shall love the Lord, with all your heart. You shall love Him more than you love your loved ones. You shall long for Him, you shall not forget yourself so that, in everything, you search for what He wants most from you.
You shall love the Lord, with all your mind. You shall devote the best of your intelligence to knowing Him. Looking into your own life, you shall understand how much He has guided you. You shall try to understand how the kingdom of God is coming through world and daily events. Praying and reading the Bible regularly, you shall ask God to give you His own Spirit so that you may understand Him better.
You shall love the Lord, with all your strength. Since you are very weak in this, you shall ask for His help and strive to unite with the true servants of God, using the means that the Church makes available to you.