The Church is considered to have had her “birth” at Pentecost. This was when the Holy Spirit descended on the faithful, just as it descends in the Sacrament of Confirmation. In receiving this “sacrament of Christian initiation,” we complete what began in Baptism. That is, Confirmation brings an increase and deepening of baptismal grace. The Greek word “Christ” means “anointed one,” and in Confirmation, we too are anointed, so that we are made fully “Christian” ourselves. We receive the fullness of the Holy Spirit, including the gifts of the Holy Spirit, and we become adults in the Faith. Confirmation does not mark the end of the process of religious education; Confirmation instead radically changes us, such that it is the beginning of a new life in the Faith.
OK, so what does that mean??The concept of Confirmation might be difficult to grasp at first; we might not understand its importance or how it might change us. Thus, as an example, it might be helpful to consider in context how it changed the faithful at Pentecost. Before then, the Apostles and disciples had abandoned Jesus – they ran away when Jesus was arrested, and they hid in fear when Jesus was tried and crucified. Even after the resurrection, they were afraid to go out in public. But after the Holy Spirit descended upon them at Pentecost, after their “confirmation,” they were given the grace and strength and perseverance to go out and spread the Good News and even endure persecution. With these graces of the Holy Sprit, especially the gift of fortitude, they were able to do what they otherwise could not do on their own. It is by such graces of the Holy Spirit that the Apostles and others were able to endure sufferings, tortures, and martyrdom (the word “martyr” is Greek, and it means “witness”).
So, too, your Confirmation will strengthen you, and you will be made soldiers of Christ in order to fulfill your duty of witnessing to and defending the Faith. If you accept in your heart and cooperate with the supernatural gifts of the Holy Spirit that are imparted by the Sacrament, you will also be affected in a particular practical way, that is, by working with the gifts given to you, you will more easily bear certain “fruits” of the Holy Spirit. By embracing the gifts of wisdom, understanding, counsel, fortitude, knowledge, piety, and fear of the Lord, we are more able to experience the fruits of love (charity), joy, peace, patience, kindness, goodness, generosity, faithfulness, gentleness, modesty, self-control, and chastity. Likewise, these gifts help a person attain sanctification and bring to perfection virtues -- both the theological virtues (faith, hope, and charity) and the cardinal virtues (prudence, justice, fortitude, and temperance).
Now, it may also appear after receiving the Sacrament that nothing has happened, that you are the same as before. If no one breaks out speaking in tongues, you may be tempted to conclude that you have not received any graces. But do not be misled by such superficial appearances. By the Sacrament, your very being is altered in a fundamental way. As with the Eucharist, you may look the same, but you are radically transformed by the fire of the Holy Spirit; an indelible spiritual mark or seal is left. This seal of the Holy Spirit marks our total belonging to Christ. We may not notice because sin and the contemporary world have so corrupted us that we cannot always immediately recognize God’s presence within us. But He is present nonetheless. If even only as a seed, the Holy Spirit, if you accept Him, will dwell within you and graces will grow within you, and, like the Apostles, disciples, martyrs, and saints, you will be able to do that which is impossible to do on your own.
But a gift, any gift, is not completed and is completely useless unless it is accepted by the recipient. If a gift is simply put in a closet, unopened, it is as if it was never received. Thus, it is necessary that you accept those graces and the gifts of the Holy Spirit. Although Confirmation alters our very nature by leaving an indelible spiritual mark upon us, grace from God presupposes nature, it does not replace it. God does not simply override our will and wipe out our humanity in offering us His grace. He does not impose Himself upon us against our will and treat us as puppets. Rather, grace builds on and works within our nature to heal it, to perfect, elevate, and transform it. We must allow the Holy Spirit and gift of grace to come into our hearts, and not simply set that grace aside and ignore it. If we resist and ignore those graces, if we shut ourselves off from the Truth and Love which are the Holy Spirit, then life becomes much harder and unsatisfactory. If we turn away from the Light, it is much more difficult to find our way through life in the darkness.
As St. Ambrose wrote, “Recall then that you have received the spiritual seal, the spirit of wisdom and understanding, the spirit of right judgment and courage, the spirit of knowledge and reverence, the spirit of holy fear in God's presence. Guard what you have received. God the Father has marked you with his sign; Christ the Lord has confirmed you and has placed his pledge, the Spirit, in your hearts.”
Meanwhile, St. Thomas Aquinas explained the Sacrament of Confirmation this way --
Summa Theologica III, q. 72
art. 1 * * * Christ instituted this sacrament not by bestowing, but by promising it, according to Jn. 16:7: "If I go not, the Paraclete will not come to you, but if I go, I will send Him to you." And this was because in this sacrament the fullness of the Holy Ghost is bestowed, which was not to be given before Christ's Resurrection and Ascension; according to Jn. 7:39: "As yet the Spirit was not given, because Jesus was not yet glorified." * * *
Those who receive Confirmation, which is the sacrament of the fullness of grace, are conformed to Christ, inasmuch as from the very first instant of His conception He was "full of grace and truth" (John 1:14). This fullness was made known at His Baptism, when "the Holy Ghost descended in a bodily shape . . . upon Him" (Luke 3:22).
art. 5 * * * just as Baptism is a spiritual regeneration unto Christian life, so also is Confirmation a certain spiritual growth bringing man to perfect spiritual age. But it is evident, from a comparison with the life of the body, that the action which is proper to man immediately after birth, is different from the action which is proper to him when he has come to perfect age. And therefore, by the sacrament of Confirmation man is given a spiritual power in respect of sacred actions other than those in respect of which he receives power in Baptism. For in Baptism he receives power to do those things which pertain to his own salvation, forasmuch as he lives to himself: whereas in Confirmation he receives power to do those things which pertain to the spiritual combat with the enemies of the Faith. This is evident from the example of the apostles, who, before they received the fullness of the Holy Ghost, were in the "upper room . . . persevering . . . in prayer" (Acts 1:13-14); whereas afterwards they went out and feared not to confess their faith in public, even in the face of the enemies of the Christian Faith. And therefore it is evident that a character is imprinted in the sacrament of Confirmation.
art. 6. The character of Confirmation, of necessity supposes the baptismal character: so that, in effect, if one who is not baptized were to be confirmed, he would receive nothing, but would have to be confirmed again after receiving Baptism. The reason of this is that, Confirmation is to Baptism as growth to birth, as is evident from what has been said above. Now it is clear that no one can be brought to perfect age unless he be first born: and in like manner, unless a man be first baptized, he cannot receive the sacrament of Confirmation.
The Divine power is not confined to the sacraments. Hence man can receive spiritual strength to confess the Faith of Christ publicly, without receiving the sacrament of Confirmation: just as he can also receive remission of sins without Baptism. Yet, just as none receive the effect of Baptism without the desire of Baptism; so none receive the effect of Confirmation, without the desire of Confirmation.
art. 7. In this sacrament, as stated above (1 and 4), the Holy Ghost is given to the baptized for strength: just as He was given to the apostles on the day of Pentecost, as we read in Acts 2; and just as He was given to the baptized by the imposition of the apostles' hands, as related in Acts 8:17. * * * the Holy Ghost is not sent or given except with sanctifying grace. Consequently it is evident that sanctifying grace is bestowed in this sacrament.
Sanctifying grace does indeed take away sin; but it has other effects also, because it suffices to carry man through every step as far as eternal life. * * * Therefore sanctifying grace is given not only for the remission of sin, but also for growth and stability in righteousness.
Further, as appears from its very name, this sacrament is given in order "to confirm" what it finds already there. And consequently it should not be given to those who are not in a state of grace. For this reason, just as it is not given to the unbaptized, so neither should it be given to the adult sinners, except they be restored by Penance.