Catechism of the Catholic Church

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'.68 The Holy Spirit is thus revealed as another divine person with Jesus and the Father".

244 "The eternal origin of the Holy Spirit is revealed in his mission in time. The Spirit is sent to the apostles and to the Church both by the Father in the name of the Son, and by the Son in person, once he had returned to the Father.69 The sending of the person of the Spirit after Jesus' glorification70 reveals in its fullness the mystery of the Holy Trinity".