CCC 462 The Letter to the Hebrews refers to the same mystery:
Consequently, when Christ came into the world, he said, “Sacrifices and offerings you have not desired, but a body have you prepared for me; in burnt offerings and sin offerings you have taken no pleasure. Then I said, Lo, I have come to do your will, O God.”1

CCC 488 “God sent forth his Son”, but to prepare a body for him,2 he wanted the free co-operation of a creature. For this, from all eternity God chose for the mother of his Son a daughter of Israel, a young Jewish woman of Nazareth in Galilee, “a virgin betrothed to a man whose name was Joseph, of the house of David; and the virgin’s name was Mary”:3
The Father of mercies willed that the Incarnation should be preceded by assent on the part of the predestined mother, so that just as a woman had a share in the coming of death, so also should a woman contribute to the coming of life.4

CCC 606 The Son of God, who came down “from heaven, not to do [his] own will, but the will of him who sent [him]”,5 said on coming into the world, “Lo, I have come to do your will, O God.” “And by that will we have been sanctified through the offering of the body of Jesus Christ once for all.”6 From the first moment of his Incarnation the Son embraces the Father’s plan of divine salvation in his redemptive mission: “My food is to do the will of him who sent me, and to accomplish his work.”7 The sacrifice of Jesus “for the sins of the whole world”8 expresses his loving communion with the Father. “The Father loves me, because I lay down my life”, said the Lord, “[for] I do as the Father has commanded me, so that the world may know that I love the Father.”9

CCC 614 This sacrifice of Christ is unique; it completes and surpasses all other sacrifices.10 First, it is a gift from God the Father himself, for the Father handed his Son over to sinners in order to reconcile us with himself. At the same time it is the offering of the Son of God made man, who in freedom and love offered his life to his Father through the Holy Spirit in reparation for our disobedience.11

CCC 1540 Instituted to proclaim the Word of God and to restore communion with God by sacrifices and prayer,12 this priesthood nevertheless remains powerless to bring about salvation, needing to repeat its sacrifices ceaselessly and being unable to achieve a definitive sanctification, which only the sacrifice of Christ would accomplish.13

CCC 2568 In the Old Testament, the revelation of prayer comes between the fall and the restoration of man, that is, between God’s sorrowful call to his first children: “Where are you?. .. What is this that you have done?”14 and the response of God’s only Son on coming into the world: “Lo, I have come to do your will, O God.”15 Prayer is bound up with human history, for it is the relationship with God in historical events.

CCC 2824 In Christ, and through his human will, the will of the Father has been perfectly fulfilled once for all. Jesus said on entering into this world: “Lo, I have come to do your will, O God.”16 Only Jesus can say: “I always do what is pleasing to him.”17 In the prayer of his agony, he consents totally to this will: “not my will, but yours be done.”18 For this reason Jesus “gave himself for our sins to deliver us from the present evil age, according to the will of our God and Father.”19 “And by that will we have been sanctified through the offering of the body of Jesus Christ once for all.”20

1 Heb 10:5-7, citing Ps 40:6-8 ([7-9] LXX).
2 Gal 4:4; Heb 10:5.
3 Lk 1:26-27.
4 LG 56; cf. LG 61.
5 Jn 6:38.
6 Heb 10:5-10.
7 Jn 4:34.
8 1 Jn 2:2.
9 Jn 10:17; 14:31.
10 Cf. Heb 10:10.
11 Cf. Jn 10:17-18; 15:13; Heb 9:14; 1 Jn 4:10.
12 Cf. Mal 2:7-9.
13 Cf. Heb 5:3; 7:27; 101-4.
14 Gen 3:9, 13.
15 Heb 10:5-7.
16 Heb 10:7; Ps 40:7.
17 Jn 8:29.
18 Lk 22:42; cf. Jn 4:34; 5:30; 6:38.
19 Gal 1:4.
20 Heb 10:10.