This Holy day of Obligation, 40th day of Easter, commemorates Christ's Ascension into Heaven from Mount Olivet 40 days after He rose from the dead (Mark 16:14-20). After the Gospel is sung, the Paschal Candle, lit from the New Fire of the Easter Vigil, is extinguished to symbolize the departure of Christ (if you use a Paschal candle at home, it should be put away today, too).
I. The Ascension completes our faith in Him, who was God as well as man
The mystery of our salvation, dearly-beloved, which the Creator of the universe valued at the price of His blood, has now been carried out under conditions of humiliation from the day of His bodily birth to the end of His Passion. And although even in "the form of a slave" many signs of Divinity have beamed out, yet the events of all that period served particularly to show the reality of His assumed Manhood. But after the Passion, when the chains of death were broken, which had exposed its own strength by attacking Him, Who was ignorant of sin, weakness was turned into power, mortality into eternity, contumely into glory, which the Lord Jesus Christ showed by many clear proofs in the sight of many, until He carried even into heaven the triumphant victory which He had won over the dead. As therefore at the Easter commemoration, the Lord's Resurrection was the cause of our rejoicing; so the subject of our present gladness is His Ascension, as we commemorate and duly venerate that day on which the Nature of our humility in Christ was raised above all the host of heaven, over all the ranks of angels, beyond the height of all powers, to sit with God the Father. On which Providential order of events we are founded and built up, that God's Grace might become more wondrous, when, notwithstanding the removal from men's sight of what was rightly felt to command their awe, faith did not fail, hope did not waver, love did not grow cold. For it is the strength of great minds and the light of firmly-faithful souls, unhesitatingly to believe what is not seen with the bodily sight, and there to fix one's affections whither you cannot direct your gaze. And whence should this Godliness spring up in our hearts, or how should a man be justified by faith, if our salvation rested on those things only which lie beneath our eyes? Hence our Lord said to him who seemed to doubt of Christ's Resurrection, until he had tested by sight and touch the traces of His Passion in His very Flesh, "because you have seen Me, you have believed: blessed are they who have not seen and yet have believed John 20:29 ."
II. The Ascension renders our faith more excellent and stronger
In order, therefore, dearly-beloved, that we may be capable of this blessedness, when all things were fulfilled which concerned the Gospel preaching and the mysteries of the New Testament, our Lord Jesus Christ, on the fortieth day after the Resurrection in the presence of the disciples, was raised into heaven, and terminated His presence with us in the body, to abide on the Father's right hand until the times Divinely fore-ordained for multiplying the sons of the Church are accomplished, and He comes to judge the living and the dead in the same flesh in which He ascended. And so that which till then was visible of our Redeemer was changed into a sacramental presence , and that faith might be more excellent and stronger, sight gave way to doctrine, the authority of which was to be accepted by believing hearts enlightened with rays from above.
III. The marvellous effects of this faith on all
This Faith, increased by the Lord's Ascension and established by the gift of the Holy Ghost, was not terrified by bonds, imprisonments, banishments, hunger, fire, attacks by wild beasts, refined torments of cruel persecutors. For this Faith throughout the world not only men, but even women, not only beardless boys, but even tender maids, fought to the shedding of their blood. This Faith cast out spirits, drove off sicknesses, raised the dead: and through it the blessed Apostles themselves also, who after being confirmed by so many miracles and instructed by so many discourses, had yet been panic-stricken by the horrors of the Lord's Passion and had not accepted the truth of His resurrection without hesitation, made such progress after the Lord's Ascension that everything which had previously filled them with fear was turned into joy. For they had lifted the whole contemplation of their mind to the Godhead of Him that sat at the Father's right hand, and were no longer hindered by the barrier of corporeal sight from directing their mind.' gaze to That Which had never quitted the Father's side in descending to earth, and had not forsaken the disciples in ascending to heaven.