The importance of marriage is seen throughout salvation history, as the Catechism of the Catholic Church (CCC) affirms:
1602 Sacred Scripture begins with the creation of man and woman in the image and likeness of God and concludes with a vision of “the wedding-feast of the Lamb.” Scripture speaks throughout of marriage and its “mystery,” its institution and the meaning God has given it, its origin and its end, its various realizations throughout the history of salvation, the difficulties arising from sin and its renewal “in the Lord” in the New Covenant of Christ and the Church (footnotes omitted).
In addition, we see the fundamental importance of consent in making a marriage in the first marriage in human history. Adam’s “yes” to God re: the matrimonial gift of Eve is seen in his response to God: “This at last is bone of my bones and flesh of my flesh; she shall be called Woman, because she was taken out of Man” (Genesis 2:23). Eve’s consent is implied in Scripture, as we see her freely living with her husband and raising a family.
In the Church’s Code of Canon Law, the Church explains why consent is fundamental and indispensable in making a marriage:
Can. 1057 §2. Matrimonial consent is an act of the will by which a man and a woman mutually give and accept each other through an irrevocable covenant in order to establish marriage.
In other words, consent is fundamental to the exchange of a couple’s wedding vows, without which you can’t have marital commitment. Again, that’s been fundamental since the first marriage in human history, and it’s logically carried over to the Sacrament of Christian Marriage, as the Church adds well in the CCC:
1626 The Church holds the exchange of consent between the spouses to be the indispensable element that “makes the marriage.” If consent is lacking there is no marriage.
1627 The consent consists in a “human act by which the partners mutually give themselves to each other”: “I take you to be my wife” – “I take you to be my husband.” This consent that binds the spouses to each other finds its fulfillment in the two “becoming one flesh” (footnotes omitted).
Jesus Christ highlights the importance of consent—and does so in elevating human marriage to a sacrament between two Christians—by uniting himself to his mystical bride the Church:
In the Latin Rite the celebration of marriage between two Catholic faithful normally takes place during Holy Mass, because of the connection of all the sacraments with the Paschal mystery of Christ. In the Eucharist the memorial of the New Covenant is realized, the New Covenant in which Christ has united himself for ever to the Church, his beloved bride for whom he gave himself up. It is therefore fitting that the spouses should seal their consent to give themselves to each other through the offering of their own lives by uniting it to the offering of Christ for his Church made present in the Eucharistic sacrifice, and by receiving the Eucharist so that, communicating in the same Body and the same Blood of Christ, they may form but “one body” in Christ (CCC 1621; footnotes omitted).
For more on this issue, see CCC 1622-28.