I would like to start answering the question: Why do we need the Holy Spirit?
The plan of salvation is fulfilled with the sending of the Holy Spirit from the standpoint of God himself. Our side starts there. If we look at the apostles lives and fears, we see that even though they follow Jesus, and they witness the passion, death and resurrection, that is not enough to remove all their fears and make them strong. We need something, someone more: The Holy Spirit. As St. Paul affirmed: “For all who are led by the Spirit of God are sons of God. For you did not receive the spirit of slavery to fall back into fear, but you have received the spirit of sonship, which enables us to cry out, ‘Abba, Father’” (Rom 8:14-15).
It is the Spirit of God who makes them and us understand the profound meaning of the mysteries of Jesus’ life and doing that gives us a new perspective of the plan of salvation, of our lives, and of the world in which we live, filling our minds and hearts. These two elements are necessary to be instruments in the evangelization. Understanding the mysteries of our life, and of the life of Jesus, with a heart open to love the message of the Gospel is possible only with the help of the Holy Spirit. That is why we need the Holy Spirit.
In Pentecost the apostles received a new strength so great that they were able to proclaim Christ’s Resurrection in different languages: “They were all filled with the Holy Spirit, and began to speak in other tongues, as the Spirit gave them utterance” (Acts 2:4). 
Through all that time after the resurrection, they were not alone, even after the ascension. Mary was with them, in the same way that She is always with the Church and with us, preparing us to receive the Spirit of God, in order to transform the world, as we sing in the Psalm: Lord, send out your Spirit, and renew the face of the earth.
All renewal begins with a transformation of ourselves, and transcends us to extend the effect to the society in which we live, without making differences according to race, religion, or status. See how it is described in the second reading: For in one Spirit we were all baptized into one body, whether Jews or Greeks, slaves or free persons, and we were all given to drink of one Spirit.
It is because of the Spirit that we can fulfill the commandment of Jesus to Preach the gospel to all the ends of the earth, in freedom and without fear. I am asking you to pray to be open to the Spirit, that He will guide us and our community, in the same way He guided the apostles and continues to inspire and guide our Church.

Fr. Sergio