CIC 201 To Israel, his chosen, God revealed himself as the only One: “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 might.”1 Through the prophets, God calls Israel and all nations to turn to him, the one and only God: “Turn to me and be saved, all the ends of the earth! For I am God, and there is no other. .. To me every knee shall bow, every tongue shall swear. ‘Only in the LORD, it shall be said of me, are righteousness and strength.’”2

CIC 368 The spiritual tradition of the Church also emphasizes the heart, in the biblical sense of the depths of one’s being, where the person decides for or against God.3

CIC 459 The Word became flesh to be our model of holiness: “Take my yoke upon you, and learn from me.” “I am the way, and the truth, and the life; no one comes to the Father, but by me.”4 On the mountain of the Transfiguration, the Father commands: “Listen to him!”5 Jesus is the model for the Beatitudes and the norm of the new law: “Love one another as I have loved you.”6 This love implies an effective offering of oneself, after his example.7

CIC 708 This divine pedagogy appears especially in the gift of the Law.8 God gave the Law as a “pedagogue” to lead his people toward Christ.9 But the Law’s powerlessness to save man deprived of the divine “likeness,” along with the growing awareness of sin that it imparts,10 enkindles a desire for the Holy Spirit. The lamentations of the Psalms bear witness to this.

CIC 2055 When someone asks him, “Which commandment in the Law is the greatest?”11 Jesus replies: “You shall love the Lord your God with all your heart, and with all your soul, and with all your mind. This is the greatest and first commandment. And a second is like it: You shall love your neighbor as yourself. On these two commandments hang all the Law and the prophets.”12 The Decalogue must be interpreted in light of this twofold yet single commandment of love, the fullness of the Law:
The commandments: “You shall not commit adultery, You shall not kill, You shall not steal, You shall not covet,” and any other commandment, are summed up in this sentence: “You shall love your neighbor as yourself.” Love does no wrong to a neighbor; therefore love is the fulfilling of the law.13

CIC 2083 Jesus summed up man’s duties toward God in this saying: “You shall love the Lord your God with all your heart, and with all your soul, and with all your mind.”14 This immediately echoes the solemn call: “Hear, O Israel: the LORD our God is one LORD.”15
God has loved us first. The love of the One God is recalled in the first of the “ten words.” The commandments then make explicit the response of love that man is called to give to his God.

CIC 2093 Faith in God’s love encompasses the call and the obligation to respond with sincere love to divine charity. The first commandment enjoins us to love God above everything and all creatures for him and because of him.16

CIC 2196 In response to the question about the first of the commandments, Jesus says: “The first is, ‘Hear, O Israel: The Lord our God, the Lord is one; 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.’ The second is this, ‘You shall love your neighbor as yourself.’ There is no other commandment greater than these.”17
The apostle St. Paul reminds us of this: “He who loves his neighbor has fulfilled the law. The commandments, ‘You shall not commit adultery, You shall not kill, You shall not steal, You shall not covet,‘ and any other commandment, are summed up in this sentence, ‘You shall love your neighbor as yourself.’ Love does no wrong to a neighbor; therefore love is the fulfilling of the law.”18

1 Dt 6:45.
2 Is 45:22-24; cf. Phil 2:10-11.
3 Cf. Jer 31:33; Dt 6:5; 29:3; Is 29:13; Ezek 36:26; Mt 6:21; Lk 8:15; Rom 5:5.
4 Mt 11:29; Jn 14:6.
5 Mk 9:7; cf. Dt 6:4-5.
6 Jn 15:12.
7 Cf. Mk 8:34.
8 Cf. Ex 19-20; Deut 1-11; 29-30.
9 Gal 3:24.
10 Cf. Rom 3:20.
11 Mt 22:36.
12 Mt 22:37-40; cf. Deut 6:5; Lev 19:18.
13 Rom 13:9-10.
14 Mt 22:37; cf. Lk 10:27:“... and with all your strength.”
15 Deut 6:4.
16 Cf. Deut 6:4-5.
17 Mk 12:29-31; cf. Deut 6:4-5; Lev 19:18; Mt 22:34-40; Lk 10:25-28.
18 Rom 13:8-10.