Apostle John mentioned "first day" in John 20:
There is 7 other places with the phrase "first day of the week".
All 8 of them is the "first work day" of the week in the n.t..
Later, the same John also mentioned "Lord's Day" in Revelation 1:
This message originated with the Father, who gave it to Christ;
then Christ gave it to an angel, and an angel reveled it to John.
There is also words in red-letters that Christ added Himself.
We know Jesus is the spirit of prophecy.
Revelation means the act of revealing or disclosing something.
The book of Revelation is/has prophecy disclosed in it. This book
gives us a timeframe, or a time sequence for prophecy in other books.
7Behold, he cometh with clouds; and every eye shall see him,
and they also which pierced him: and all kindreds of the earth
shall wail because of him. Even so, Amen.
This day mentioned was not a day per say like Sunday or Saturday.
The "Lord's Day" is The theme of the book of revelations. The time
frame right before Christ returns to earth. Elsewhere in the bible,
this same time frame "right before Christ returns" is called
"the day of the Lord". Some 30 verses deal with this time frame.
Search results for: the day of the Lord
www.bible.com
The Day of the Lord is actually a year long event.
"For it is the day of the LORD 's vengeance, and the year
of recompences for the controversy of Zion. Isaiah 34:8 (KJV)
Some verses cover before, during, and just after His Return. For
example Zechariah 12:8 "
In that day" is in this one year period.
8In that day shall the LORD defend the inhabitants of Jerusalem;"..
.
"He that hath an ear, let him hear what the Spirit saith unto the
churches; To him that overcometh will I give to eat of the tree
of life, which is in the midst of the paradise of God Rev. 2:7.
Revelation 2:11, Revelation 2:17, Revelation 2:29,
Revelation 3:22, Revelation 3:6, Revelation 3:13.
Was the first day of the week also called the Lord's Day?
Never in the bible that I know of. Is there any verse that tell us to keep
the "first day of the week", or this "Lords day" anywhere in the bible?
NT alone does not say that explicitly.
There is no connection to the first day of the week
and the Lords day at all anywhere in the bible.
I think the Lord's Day was more likely the first day of the week than any other day of the week.
I think as shown above it was not any specific day of the week.