Sacraments are outward signs, instituted by Christ to give us grace which is a share in God's own life.
"The purpose of the sacraments is to sanctify men, to build up the Body of Christ and, finally, to give worship to God. Because they are signs they also instruct. They not only presuppose faith, but by words and objects they also nourish, strengthen, and express it. That is why they are called 'sacraments of faith." CCC #1123
Celebrated worthily in faith, the sacraments confer the grace that they signify. They are efficacious because in them Christ himself is at work: it is he who baptizes, he who acts in his sacraments in order to communicate the grace that each sacrament signifies. The Father always hears the prayer of his Son's Church which, in the epiclesis of each sacrament, expresses her faith in the power of the Spirit. As fire transforms into itself everything it touches, so the Holy Spirit transforms into the divine life whatever is subjected to his power. CCC #1127
These "mysteries" are seven in number: