The Third Glorious Mystery of the Rosary is the Descent of the Holy Spirit on Pentecost Sunday, ten days after the Ascension. The fruit most commonly associated with the mystery of the Descent of the Holy Spirit is the gifts of the Holy Spirit.
Meditation on the Descent of the Holy Spirit:
"And they were all filled with the Holy Ghost, and they began to speak with divers tongues, according as the Holy Ghost gave them to speak" (Acts 2:4). After the Ascension, the Apostles had gathered with the Mother of God in the upper room. For nine days they had prayed, and now their prayers are being answered. The Holy Spirit, like a mighty wind, like tongues of fire, has come upon them, and just as at the Annunciation, when the Spirit of the Most High overshadowed Mary, our world is forever changed.
Christ had promised not to leave them—us—alone. He would send His Spirit, "the Spirit of truth," to "teach you all truth" (John 16:13). Here in this upper room, the Church is born, baptized in the Spirit and endowed with the truth. And that Church becomes for us not only Mother and Teacher, the certain measure of truth, but the conduit of the Spirit. Through Her, through the Sacraments of Baptism and Confirmation, we receive the gifts of the Holy Spirit. The Holy Spirit descends upon us as He did upon them, through the Church that He gave birth to on that day.