Saturday of the 4th Week of Easter
Omnipotens sempiterne Deus,
semper in nobis paschale perfice sacramentum
ut quos sacro baptismate dignatus es renovare,
sub tuae protectionis auxilio multos fructus afferant,
et ad aeternae vitae gaudia pervenire concedas.
This was not in any previous edition of the Roman Missal. A precedent was in the Sacramentarium Bergomense.
Almighty eternal God,
perfect in us always the paschal mystery,
so that they whom you deigned to renew by means of sacred baptism,
may under the aid of Your protection bear many fruits,
and that you will grant them to attain unto the joys of eternal life.
There are some interesting things here. First, perfice as the imperative "perfect" has the force of "bring to completion". It could be perceived as "perfect" in an instant of time, by a sudden and all embracing act, or it could be construed as being an ongoing process of perfection, of bringing to completion. In a way the Paschale Mystery itself (remember that mysterium and sacramentum are pretty much interchangeable in these contexts) reflects this same problem of our perception of time and God’s work in time, or outside of time, or beyond time. The Paschal Mystery is both completed and not completed. Our redemption is "already" completed, but "not yet" completed. As Christians we live in this pilgrim life, this earthly continuum, in a constant state of "already but not yet".
We have some time to look at the word sempiterne. This is a vocative form of sempiternus, a, um. In philosophy and theology (mostly indistinguishable in ancient times through late antiquity) there has been constant effort to figure out time and God’s relationship to time. In this prayer sempiternus is simply the equivalent of aeternus, "eternal". Scripture has innumerable references to God being aeternus and it is associated with God’s unchanging nature. There are some 50 or so prayers in the Missal which begin with today’s formula and many that start with aeterne Deus.
Even thought the words are pretty much interchangeable in our prayers, eternity and sempiternity are really different concepts. Eternity can be thought of different ways. First, eternity can be completely independent of time. Something eternal in this sense is entirely outside of time. St. Augustine, who was a Neoplatonist in this sense, thought of God this way. Another eternity is everlastingness. It has no beginning or end. This is what we call sempiternity. That is to say, it exists at "all points in time". This is a great simplification of a millennial discussion, but it can give you a quick glimpse into this language of prayer. The Greeks, from Parmeides to Plato to Plotinus all wrote about eternity. Christian ideas of eternity were explored by authors like St. Augustine (+430), Boethius (+c.526), Eriugena (+c.877), St. Anselm (+1109), St. Thomas Aquinas (+1274). When we say in these prayers that God is sempiternus we do not thereby believe as Catholics that God is "everlasting" in the sense of being in time, that is all points of time, but without beginning or end. God is eternal in the sense of being beyond time, entirely transcending time.
Finally, there is in this prayer a reference to Joh 15:16: Non vos me elegistis sed ego elegi vos et posui vos ut eatis et fructum adferatis et fructus vester maneat ut quodcumque petieritis Patrem in nomine meo det vobis… You have not chosen me: but I have chosen you; and have appointed you, that you should go and should bring forth fruit; and your fruit should remain: that whatsoever you shall ask of the Father in my name, he may give it you.