If we wish to obtain a supernatural end, we should avail ourselves of the supernatural means instituted by God for obtaining that end. Catholics believe that the sacraments are one of the means to such an end. The end to be obtained, in the case of sacraments, is sanctity. The Catechism of the Council of Trent defines a sacrament as: "Something perceptible by the senses which by Divine institution has the power both to signify and to effect sanctity. . .." Three things are necessary: an outward sign (e.g., water as in the case of baptism), grace and Divine institution (i.e., God has to have created the sacrament). Note too, that the person must be properly disposed to recieve the grace given in the sacrament, or stated differently, if the person intentionally places an obstacle in the way of the grace being infused, then the grace will not flow to the person. For example, in the case of the sacrament of confession, if contrition is absent in the penitent, the sacrament will not "work" -- the grace will not flow. Faith and human will need to work in cooperation with God's free gift of grace in order to make the sacraments efficacious.
There are seven sacraments. Two are the sacraments of the dead and five are the sacraments of the living. The sacraments of the dead are baptism and confession. They are called sacraments of the dead because the effect of those sacraments is to remove what is dead in us, namely sin. The sacraments of the living are confirmation, eucharist, marriage, priestly ordination and annointing of the sick. In order to receive one of the five sacraments of the living, the recipient must be in a state of grace (i.e., not in a state of mortal sin). If one is properly disposed, the grace will in fact be conferred. It is not a "sometimes" thing, it is an "every time" thing and therein lies the power and the awe. Think about it for a minute. If you ask, in the case of the sacraments, for grace, and you follow the means laid down by Christ for getting the grace, you WILL get it. That is a little hard to comprehend, but comprehend and partake, we must.
For the believer, reception of the sacraments, including frequent and regular reception of those sacraments that can be received more than once (e.g., confession, eucharist), is the manner in which participation in the life of Christ is made most fully possible. This is so, again, because the supernatural end that is being sought is holiness. All Christians believe that following Christ and seeking to do his will (i.e., seeking to be more holy -- even if we fall short -- and we do) results in a closer relationship with Him. The grace that He pours into our hearts also has a healing effect in our lives by removing the stain of sin and the later proclivity to commit sin. Wow!
Proofs of the dogma of the sacraments are not found in Scripture alone, but in Scripture and Sacred Tradition. In Sacred Scripture we find expressions which clearly indicate that the sacraments are more than mere signs of grace and faith: "Unless a man be born again of water and the Holy Spirit, he cannot enter into the kingdom of God" (John 3:5); "He saved us, by the laver of regeneration, and renovation of the Holy Spirit" (Titus 3:5); "Then they laid their hands upon them, and they received the Holy Spirit" (Acts 8:17); "He that eateth my flesh, and drinketh my blood, hath everlasting life. For my flesh is food indeed: and my blood is drink indeed" (John 6:55-56). For Sacred Tradition's part, it is enough to say that the Church has, since Christ created the Church, confected the sacraments in the same manner. There is nothing new under the sun here -- Christ taught the apostles how to do it and the Holy Spirit has safeguarded those teachings down through the ages to the present day. A quick review of the writings of the early Fathers of the Church makes this abundantly clear.
It is important to mention that the sacraments are not the only means of receiving God's grace and to suggest otherwise would be to foolishly place limits on the omnipotence of God. It is sufficient to say that the sacraments were instituted by God as an ordinary, but not the only, way of conferring grace.
For more exegesis on the subject of the sacraments, see the Official Catholic Encyclopedia.
