Believing in the Spirit
From the Catechism of the Catholic Church, Simplified
Hidden - Yet Known by His Works (687-688)
Although the Spirit reveals Christ and makes us hear the Father's Word, we do not hear the Spirit himself because he "will not speak on his own" (Jn 16:13). Because of this "divine self-effacement," the world "cannot receive him because it neither sees him nor knows him." Believers, however, know the Spirit because he dwells in them (Jn 14:17).
The Spirit inspired the Scriptures, gave us Tradition, assists the Church's Magisterium, gives us communion with Christ through the sacraments, intercedes in prayer, bestows charisms and ministries, inspires missionary life, and witnesses through the saints.
The Son and Spirit Working Together (689-690)
The Spirit is truly God, consubstantial and inseparable from the Father and the Son (both in their inner life and in their work). When the Father sends his Son, he also sends his Breath. Distinct but inseparable, both have a joint mission. The Son is seen and the Spirit reveals the Son.
When Christ was glorified, he could send the Spirit (Jn 7:19) and give his glory to believers. This joint mission (of Christ and the Spirit) is manifested in the children adopted by the Father who are united to Christ by the Spirit.
"Just as there is no distance between the body and the anointing oil, so there is no distance nor intermediary between the Son and the Spirit. Contact with the Son requires contact with the oil because every part is covered with the Spirit's anointing" (St. Gregory of Nyssa).