History of the Sabbath and First Day of the Week - John N. Andrews

For these and other such circumstances the Lord’s
Day is distinguished; and therefore the holy doctors
of the church have decreed that all the glory of the
Jewish Sabbath is transferred to it. Let us therefore
keep the Lord’s Day as the ancients were
commanded to do the Sabbath."[71]
It is to be observed that Augustine does not
assign among his reasons for first-day observance,
the change of the Sabbath by Christ or his apostles,
or that the apostles observed that day, or that John
had given it the name of Lord’s Day. These
modern first-day arguments were unknown to
Augustine. He gave the credit of the work, not to
Christ or his inspired apostles, but to the holy
doctors of the church, who, of their own accord,
had transferred the glory of the ancient Sabbath to
the venerable day of the sun. The first day of the
week was considered in the fifth century the most
proper day for giving holy orders, that is, for
ordinations, and about the middle of the century,
says Heylyn,
"A law [was] made by Leo then Pope of Rome,
622