St. Augustine said, “There can be no religious society, whether the religion be true or false, without some sacrament or visible symbol to serve as a bond of union. The importance of these sacraments cannot be overstated, and only scoffers will treat them lightly. For if piety requires them, it must be impiety to neglect them.” Augustine Through the Ages: An Encyclopedia By ed FITZGERALD
A sacrament, as defined by the Catholic Church, is a symbol – but not a symbol in that it is merely symbolic, in the way we use the term today. It is a symbol in the classical sense because it is a sign. The sacraments are specific signs that were instituted by Christ to signify and effect the sanctification of man. A sacrament is an outward sign of God’s grace that actually effects what it signifies. Augustine compares them to the sacrifices of the Old Testament. He writes, “those sacrifices signified the things which we do for the purpose of drawing near to God and inducting our neighbour to do the same. A sacrifice, therefore, is the visible sacrament or sacred sign of an invisible sacrifice.” https://rcdow.org.uk/att/files/faith/catechesis/baptism/sacraments.pdf
So, what does a sacrament signify? Sacraments signify, and actually impart, grace, the undeserved gift of God. As Peter Kreeft says in Catholic Christianity, “God’s grace is God Himself, God’s own life in our souls. For God is love, and the lover’s primary gift to the beloved is the gift of himself.” Sacraments are the way in which we become intimate with God. Catholic Christianity: A Complete Catechism of Catholic Beliefs Based on the Catechism of the Catholic Church by Peter Kreeft.