Why we keep Sunday holy which the early church kept and early fathers of the church taught, some of them becoming martyrs for truth they were teaching. One such truth is
that Sunday is the Lord’s day and not Saturday. It makes absolutely no sense to keep
Saturday holy when from earliest times Sunday was kept holy. And I’m sure God will not
hold it against some on this forum who pretend to be catholic to take Sunday as their
holy day as well.
catholic.com/thisrock/1991/9109prot.asp
Ignatius of Antioch (c. 110) wrote, “Those who walk in the ancient practices attain to newness of hope, no longer observing the Sabbath, but fashioning their lives after the Lord’s Day on which our life also arose through him, that we may be found disciples of Jesus Christ, our only teacher” (Letter to the Magnesians).
In the middle of the second century Justin Martyr explained why Sunday is the day Christians observe: “Sunday is the day on which we all gather in a common assembly, because it is the first day, the day on which God, changing darkness and matter, created the world, and it is the day on which Jesus Christ our Savior rose from the dead” (First Apology).