The Catechism in Questions & Answers

524. What does the book of Acts relate concerning Holy Sealing?

An important reference to Holy Sealing is found in Acts 8: 14 et seq.: “Now when the Apostles who were at Jerusalem heard that Samaria had received the word of God, they sent Peter and John to them, who, when they had come down, prayed for them that they might receive the Holy Spirit. For as yet He had fallen upon none of them. They had only been baptised in the name of the Lord Jesus. Then they laid hands on them, and they received the Holy Spirit.”
According to this testimony from Holy Scripture, Holy Sealing is bound to the Apostle ministry. This is also confirmed in Acts 8: 18. Simon, who had previously practised sorcery but had come to believe and was baptised (cf. Acts 8: 9, 11 et seq.), “saw that through the laying on of the Apostles’ hands the Holy Spirit was given.”
From this event it follows that the sacraments of Holy Baptism with water and Holy Sealing are clearly distinguished from one another. We find a similar account in Acts 19: 1-6. In Ephesus, there were some disciples who had only received the baptism unto repentance from John. When they came to believe in Jesus, they were first of all baptised in the name of the Lord Jesus. After this they received the gift of the Holy Spirit through the Apostles: “And when Paul had laid hands on them, the Holy Spirit came upon them.”

Baptism unto repentance: see Question 485.