This Sunday was called "Sunday in the Octave of the Ascension" before 1960.
Today we celebrate the Ascension of the Lord with righteousness, with fidelity, with devotion, with holiness and with piety, says St. Augustine, if we go up with him and hold our hearts high. Let our thoughts then be where he is, and here below it will be rest. Let us now go up with Christ in our hearts; and when his day comes, we will also follow him in body. Yet we must know that neither pride, nor greed, nor lust shall rise with Christ. If we want to follow our doctor in his ascension, we must lay down the burden of our vices and sins (Matins).
This Sunday prepares us for Pentecost. Before ascending to heaven, Jesus, at the Last Supper, promised us that He would not leave us orphans, but that He would see us His Comforting Spirit (Ev., All.) so that in all things we might glorify God through Jesus Christ (Eph.). Like the Apostles gathered in the Cenacle, we must therefore prepare ourselves, through prayer and charity (Ep.), for the holy day of Pentecost when Jesus "who is our advocate with the Father" (1st Night) will obtain for us from Him the Holy Spirit.