CCC 243

Before his Passover, Jesus announced the sending of "another Paraclete" (Advocate), the Holy Spirit. At work since creation, having previously "spoken through the prophets", the Spirit will now be with and in the disciples, to teach them and guide them "into all the truth". Cf. Gen 1:2; Nicene Creed (DS — Denzinger–Schönmetzer (Enchiridion Symbolorum)); Jn 14:17, 26; 16:13. The Holy Spirit is thus revealed as another divine person with Jesus and the Father.

Read the full chapter 1. I Believe in God the Father ¶198–421