Grant, Almighty God, that the commemoration of our Lord's death and resurrection may continually transform our lives and be manifested in our deeds; through Jesus Christ our Lord, who lives and reigns with you and the Holy Spirit, one God, now and for ever. Amen.
Our thoughts in this present life should turn on the praise of God, because it is in praising God that we shall rejoice for ever in the life to come; and no one can be ready for the next life unless he trains himself for it now. So we praise God during our earthly life, and at the same time we make our petitions to him. Our praise is expressed with joy, our petitions with yearning. We have been promised something we do not yet possess, and because the promise was made by one who keeps his word, we trust him and are glad; but insofar as possession is delayed, we can only long and yearn for it. It is good for us to persevere in longing until we receive what was promised, and yearning is over; then praise alone will remain.
Because there are these two periods of time - the one that now is, beset with the trials and troubles of this life, and the other yet to come, a life of everlasting serenity and joy - we are given two liturgical seasons, one before Easter and the other after. The season before Easter signifies the troubles in which we live here and now, while the time after Easter which we are celebrating at present signifies the happiness that will be ours in the future. What we commemorate before Easter is what we experience in this life; what we celebrate after Easter points to something we do not yet possess. This is why we keep the first season with fasting and prayer; but now the fast is over and we devote the present season to praise. Such is the meaning of the Alleluia we sing.
Both these periods are represented and demonstrated for us in Christ our head. The Lord’s passion depicts for us our present life of trial - shows how we must suffer and be afflicted and finally die. The Lord’s resurrection and glorification show us the life that will be given to us in the future.
Now therefore, brethren, we urge you to praise God. That is what we are all telling each other when we say Alleluia. You say to your neighbor, “Praise the Lord!” and he says the same to you. We are all urging one another to praise the Lord, and all thereby doing what each of us urges the other to do. But see that your praise comes from your whole being; in other words, see that you praise God not with your lips and voices alone, but with your minds, your lives and all your actions.
We are praising God now, assembled as we are here in church; but when we go on our various ways again, it seems as if we cease to praise God. But provided we do not cease to live a good life, we shall always be praising God. You cease to praise God only when you swerve from justice and from what is pleasing to God. If you never turn aside from the good life, your tongue may be silent but your actions will cry aloud, and God will perceive your intentions; for as our ears hear each other’s voices, so do God’s ears hear our thoughts.
St. Augustine of Hippo, 
From Commentary on Psalm 148
The Collect for this Friday and this passage from St. Augustine’s writings express with great clarity the truth that the Christian praises God both outwardly in words and deeds, and inwardly in thoughts and prayers. The Great 50 Days are marked liturgically with much use of the word “Alleliua!” This ancient praise-shout commands hearers to “Praise God!” But, as the General Thanksgiving tells us, we show forth God’s praise “not only with our lips, but in our lives” by “giving up ourselves” to God’s service…something that requires unanimity of the inner and outer self. That notion of continuity and simplicity is especially lifted up for us today.
As we come to the end of Eastertide, the themes of the season move ineluctably towards the active life of the Holy Spirit and the constant communion of the Christian in God, even as God is revealed to be an eternal communion of Father, Son, and Holy Spirit. This mutuality and intercommunion is dynamic, lively. It is not static or monadic. St. Augustine writes that even in the midst of our earthly journey, so fraught by trials and sins, we already breathe the air of the Kingdom, taste of its food, and speak its language. All of this results in a life in transformation, become what we breathe, eat, hear. A real Christian faith is always growing, deepening, and reaching a greater level of communion and simplicity.
Fridays in Eastertide do not include the discipline of fasting as abstinence is dispensed with for this season. But Fridays are always the Day of the Cross, regardless of the season. The Cross in Eastertide is glorious, but it also reveals the costly love of Our Savior—and the costly love of disciples responding to Him. Just as Christ Jesus was fastened to the Cross, forming a unifying bond between his body of Love and this world’s need for that Love, so must our discipleship accept with humility the necessity of a unified life, where our outer praise and practice is evermore unified to our inner thoughts, prayers, and desires. When these two things—our outer and inner selves—become truly conformed to Christ, we will be free indeed.
Eastertide gives us a foretaste of that joy and unity. When we come to Pentecost, the calendar points us to the place where the triumph must be fashioned: the daily life of discipleship. That is the arena where our laurels will be won, and where the power of the Cross will be known most dearly to us, even as we show it forth to others by living as whole and faithful Christians in private as well as in public. For the grace, strength, and courage to live in Christ this way, we turn to the Cross this (and every) Friday once more.