Sunday is the Son’s Day. So I thought once-upon-a-time in my little girl reasoning. Jesus is the Son of God. He rose from the dead on a Sunday. Hence, Sunday is Son-day. Little did I know back then that my silly little play on words was not far from the truth.
This ever-ancient-yet-ever new Catholic faith always has us looking back at our roots, looking at where we are today, and looking forward with joyful hope to the Some Day where we, Lord-willing, will meet God “face to face” (Cf. 1 Cor 13:12) in the glory of Heaven.
Looking back, we find St Jerome, a 4th century biblical exegete, who wrote: “If pagans call it the day of the sun, we willingly agree, for today the light of the world is raised, today is revealed the sun of justice with healing in his wings.”
Recalling the words of Scripture, Jerome first quotes Jesus referencing himself as “the light of the world (Cf. Jn 8:12; 9:5).” Then the prophet Malachi (Cf. Mal 3:20NAB, or Mal 4:2RSV) is echoed, describing a “sun” that does not cause burns, but “heals”.
With his own play on words, Jerome shows the people of his day (and us!) that Jesus makes Sunday no ordinary day; it is uncommon from the rest of the week.
The earliest apostolic traditions name Sunday as the day when Christians worshiped and celebrated the Lord’s Day… commemorating the resurrection of Jesus.
St Justin Martyr, a 2nd century Christian apologist, described it this way:
We all gather on the day of the sun, for it is the first day [after the Jewish sabbath, but also the first day] when God, separating matter from darkness, made the world; and on this same day Jesus Christ our Savior rose from the dead.
Gathering on Sundays was so vital to the life of the early Christians, that, the eventual listing of the Precepts of the Church  named Sunday Mass as a primary duty in one’s love and service of God.
Today, the Church continues to teach that the Resurrection is the work of a new creation: God putting aright what had gone wrong in the world. The Catechism of the Catholic Church explains this idea in paragraph 2174:
Jesus rose from the dead “on the first day of the week” (Cf. Mt 28:1; Mk 16:2; Lk 24:1; Jn 20:1.)” Because it is the “first day,” the day of Christ’s Resurrection recalls the first creation. Because it is the “eighth day” following the sabbath, it symbolizes the new creation ushered in by Christ’s Resurrection. For Christians it has become the first of all days, the first of all feasts, the Lord’s Day… Sunday.
And so I go. Every Sunday. God willing. To Mass.
There all three dimensions of past, present and future come together. I look back. I see today, and I look ahead. I come to understand the Glory Be  (Gloria Patri) prayer I learned as a child… “as it was in the beginning, is now, and ever shall be…”
It is – somehow – all present to me at once, just as Jesus is Present in the Eucharist : the original creation, the new creation, and the new creation that God is somehow making out of me every Sunday, thanks be to the Risen Jesus… whom I long to meet on that coming sunny Some Day .