Why is the Holy Chrism also called the “sacrament of confirmation”?

St. Paul the Apostle says, “Now He who establishes us with you in Christ and has anointed us is God, who also has sealed us and given us the Spirit in our hearts as a guarantee” (2 Cor. 1:21–22). St. John the Apostle also says, “Now he who keeps His commandments abides in Him, and He in him. And by this we know that He abides in us, by the Spirit whom He has given us ” (1 John 3:24 ) . St. Ambrose says, “God the Father sealed you; Christ the Lord confirmed you, and gave a pledge, the Spirit, in your hearts, as you have learned in the lesson of the Apostle.”¹⁴¹³