Roman Catholic nonsense
And Christ Himself was the one who made the first day of the week special. On the day of resurrection, when He appeared to the eleven apostles, Thomas was missing for some reason. And when the others told him that they had met with the risen Lord, he refused to believe it. Now Christ could have appeared to them again the very next day, or even later on the same day. But He chose to wait a FULL EIGHT DAYS in order to meet with Thomas. Why? He planned to establish the first day of the week as the Lord's Day, when Thomas would worship Him, and then Christians would continue to worship Him on that day.
Matthew Henry's commentary on John 20:26 is very true and very significant:
2. He deferred it so long as seven days. And why so?
(1.) That he might put a rebuke upon Thomas for his incredulity. He had neglected the former meeting of the disciples; and, to teach him to prize those seasons of grace better for the future, he cannot have such another opportunity for several days. He that slips one tide must stay a good while for another. A very melancholy week, we have reason to think Thomas had of it, drooping, and in suspense, while the other disciples were full of joy; and it was owing to himself and his own folly.
(2.) That he might try the faith and patience of the rest of the disciples. They had gained a great point when they were satisfied that they had seen the Lord. Then were the disciples glad; but he would try whether they could keep the ground they had got, when they saw no more of him for some days. And thus he would gradually wean them from his bodily presence, which they had doted and depended too much upon.
(3.) That he might put an honour upon the first day of the week, and give a plain intimation of his will, that it should be observed in his church as the Christian sabbath, the weekly day of holy rest and holy convocations. That one day in seven should be religiously observed was an appointment from the beginning, as old as innocency; and that in the kingdom of the Messiah the first day of the week should be that solemn day this was indication enough, that Christ on that day once and again met his disciples in a religious assembly. It is highly probable that in his former appearance to them he appointed them that day seven-night to be together again, and promised to meet them; and also that he appeared to them every first day of the week, besides other times, during the forty days. The religious observance of that day has been thence transmitted down to us through every age of the church. This therefore is the day which the Lord has made.