What is a Sacrament?

A Protestant friend of mine recently asked me to explain what Catholics mean by "sacrament".  Before getting into that, let's just note that Catholics and Eastern Orthodox Christians understand there to be seven sacraments:  Baptism, the Eucharist ("the Lord's Supper"), Confirmation, Holy Orders, Marriage, Reconciliation, and Anointing of the Sick.

At the root of Catholic Sacramental theology is the Incarnation. God didn’t just tell us he loves us. He took on human flesh and showed us. He didn’t just forgive us our sins in some invisible way and then tell us about it, he showed us by dying on the Cross. He didn’t just tell us about a new life, he showed us in Jesus’ Resurrection. So the principle is that God speaks to us in visible and tangible form.

We can apply this principle to each of the seven sacraments, but for now I will focus on three:

• God makes the new birth (being born again) visible in Baptism. 
• He makes receiving Christ into our lives visible in the Eucharist — receiving Christ in the form of bread and wine. 
• For those already baptized but having fallen into serious sin, he makes repentance and restoration visible in the Sacrament of Reconciliation. 

St Augustine famously defined a sacrament as an outward sign of an inward grace that does what it signifies (https://en.m.wikipedia.org/wiki/Sacrament).  We can also add that each sacrament was instituted by Christ himself, a topic for a later post.