The Catechism in Questions & Answers

473. What is the purpose of the sacraments?

The sacraments allow human beings to attain salvation: through them, human beings are adopted into the fellowship of life with God and preserved in it.
Receiving the three sacraments of Holy Baptism with water, Holy Sealing, and Holy Communion gives a human being the opportunity to be united with the Lord at the return of Christ.

Return of Christ: see Question 550. et seq.