The seven sacraments have a visible and invisible reality, a reality open to all the human senses but grasped in its God-given depths with the eyes of faith. When parents hug their children, for example, the visible reality we see is the hug. The invisible reality the hug conveys is love. We cannot "see" the love the hug expresses, though sometimes we can see its nurturing effect in the child.
The visible reality we see in the sacraments is their outward expression, the form they take, and the way in which they are administered and received. The invisible reality we cannot "see" is God's grace, his gracious initiative in redeeming us through the death and Resurrection of his Son. God's initiative is called grace because it is the free and loving gift by which he offers people a share in his life, and shows us his favor and will for our salvation. Our response to the grace of God's initiative is itself a grace or gift from God by which we can imitate Christ in our daily lives.
The saving words and deeds of Jesus Christ are the foundation of what he would communicate in the sacraments through the ministers of the Church. Guided by the Holy Spirit, the Church recognizes the existence of seven sacraments instituted by the Lord. Through the sacraments, God shares his holiness with us so that we, in turn, can make the world holier.
"The Seven Sacraments are properly ordered according to three designations.
"Baptism, Confirmation, and the Eucharist are the three sacraments of Christian Initiation, which lay the foundation for the Christian life.
"Penance and Reconciliation and the Anointing of the Sick are the sacraments of healing. Through them the Church continues, in the power of the Holy Spirit, to accomplish Christ’s work of healing and salvation among the Christian faithful.
"Holy Matrimony and Holy Orders are the sacraments at the service of communion. They confer a special mission of service to the people of God."
"Sacramental Catechesis," Committee on Evangelization and Catechesis, US Conference of Catholic Bishops