Both Old Testament and New command that loving God is to be the primary and all pervasive determination of our existence.
"Thou shalt love the LORD thy God with all thine heart, and with all thy soul, and with all thy might" (Deuteronomy 6:5).
"Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind, and with all thy strength, this is the first commandment" (Mark 12:30).
The same calling beckons us in both covenants. There is a difference, however, in how the calling is to be viewed, and how it is fulfilled. Under the law, loving God is portrayed primarily as a responsibility. Conversely, the grace and truth of the Lord Jesus Christ portrays loving God as a response.
"It shall come to pass, if ye shall hearken diligently unto My commandments which I command you this day, to love the LORD your God, and to serve Him with all your heart and with all your soul that I will give you the rain of your land in His due season, the first rain and the latter rain, that thou mayest gather in thy corn, and thy wine, and thine oil" (Deuteronomy 11:13-14).
"We love Him because He first loved us" (I John 4:19).
The law could not foster and motivate love in human hearts because it could not change human hearts. Those individuals in the Old Testament who loved God did so because they received the foreshadowings of grace that existed even under the confines of a law that "made nothing perfect" (Hebrews 7:19). The law was give to reveal the lack of love in fallen humanity. As the Apostle Paul wrote, it justified nobody, and its legal and contractual constitution whereby God and man relate to each other based on the fulfillment of if-then contingencies by both parties was doomed to crash on the rocks of human imperfection. Rather than beget love for God, Paul declared that "the letter killeth" (Romans 3:20; II Corinthians 3:6).
Under the covenant of grace and truth in Christ, the love of God blessedly precedes the calling of love for God. Our love for Him is fruit rather than root. "The love of God is shed abroad in our hearts by the Holy Spirit which is given unto us" (Romans 5:5). When we believe, the Spirit of the Christ who so loves His Father inhabits us for the purpose of freely constituting our capacity to love He who is now our Father as well. "Because ye are sons, God hath sent forth the Spirit of His Son into your hearts, crying Abba, Father" (Galatians 4:6). Our love for God is thus always the response to His love for us as we "grow in grace, and in the knowledge of our Lord and Savior Jesus Christ" (II Peter 3:18).
In our thinking and our application, the order must never be reversed. As Jude commanded, we must "keep yourselves in the love of God" (Jude 1:21). Our spiritual enemies and our fleshly tendencies will tempt us to forget, ignore and even reject the ongoing overture of love that alone leads to the symphony of love being performed in our humanity by the indwelling Holy Spirit. Indeed, the believer who genuinely loves God is the same believer who is overwhelmed by love, the love of the Lord Jesus that so fills him, thrills him and humbles him that his awareness is not of loving, but of being loved. All glory flows to the nail-scarred Feet of the One who makes possible the fulfillment of the great reason for our being. Grace freely constitutes love as response rather than responsibility, and the resulting life of self sacrifice is counted not as burden, but as privilege...
"They had called the apostles, and beaten them, they commanded that they should not speak in the name of Jesus, and let them go. And they departed from the presence of the council, rejoicing that they were counted worthy to suffer shame for His name."
"The fruit of the Spirit is love."