The Catechism in Questions & Answers

587. How did the activity of the Holy Spirit reveal itself after the death of the early Apostles?

The Holy Spirit ensured that the binding collection of writings from the Old and New Testaments (canon) could come into being.
Through the activity of the Holy Spirit, important fundamentals of Christian doctrine were formulated in large church assemblies (ecumenical councils). These include, for example, the doctrine that God is triune, that Jesus Christ is both true Man and true God, and the recognition of the decisive significance that the sacrifice of Jesus and His resurrection hold for the salvation and redemption of mankind. It can also be attributed to the activity of the Holy Spirit over the centuries that the Christian faith was able to spread around the world.

Bible, canon: see Questions 12. et seq. Council: see explanation of Question 33. Triune God: see Questions 61. et seq. Dual nature of Jesus Christ: see Questions 103. et seq.