Rev 1,10
I was in the spirit on the the Lord's Day
The Christians believe The Resurrection of the Jesus Christ occurred and started in early Christianity to Observe Sunday
knowns by them as the Lord's Days to gather and worship and then when the calendar was changed .. The day became known as Sunday.. and became known as The Day to Worship The Lord. as explain
The Hebrew Old Testament normally uses the unqualified phrase "the seventh day" to refer to days which were not the seventh day of the month, and which could not possibly have fallen on the same day of the week from year to year (e.g. Exod. 12:15,16; 13:6; Lev. 23:6-8; 13:5,6,27,32,34,51; 14:9,39; Num. 6:9; 7:1-48; 19:12,19; 28:17-25; 31:19,24; Deut. 16:1-8; Josh
6:4,15; Judg. 14:12-18; 2 Sam. 12:18; 1 Kgs. 20:29; Est. 1:10).
God Rested on the Seventh Day.. ( Genesis)
http://bible.cc/genesis/2-2.htm
.http://www.thirdmill.org/answers/answer.asp/file/99959.qna/category/th/page/questions/site/iiim
The Seventh Day was the Sabbath ( according to the Bible)
Remember the sabbath day, to keep it holy. Six days shalt thou
labour, and do all thy work: But the seventh day is the sabbath of
the LORD thy God: in it thou shalt not do any work, thou, nor thy
son, nor thy daughter, thy manservant, nor thy maidservant, nor
thy cattle, nor thy stranger that is within thy gates: For in six days
the LORD MADE heaven and earth, the sea, and all that in them
is, and rested the seventh day: wherefore the LORD blessed the
sabbath day, and hallowed it." (Exodus 20:8-11).
http://www.reformation.org/lords-day-sabbath.pdf
Thus the First Day of the Week
Mark 16.2.
2 And very early in the morning the first day of the week, they came unto the sepulchre at the rising of the sun.
http://www.ucgstp.org/htmlbible2/mar016.htm#V9
THe FIrst day of the Week .. Is Sunday.
http://ecclesia.org/truth/1st-day.html
SINCE THE LORDS DAY WAS THE FIRST DAY AND THE DAY THAT
JESUS ROSE ( BELIEVED BY SOME CHRISTIANS) THEY CHANGED THE SABBATH TO SUNDAY.
New Testament church, under the guidance of the Apostles, apparently felt the freedom to change the day of observance relative to the secular calendar. They still maintained the commanded six-day-plus-one pattern, but shifted their Sabbath observance to the first day of the week relative to the secular calendar. They chose this day most probably because it was the day on which Jesus had been raised from the dead (Matt. 28:1; Mark 16:2; Luke 25:1; John 20:1). The risen Lord also chose the first day of the week on which to manifest himself to his disciples when they were gathered together (John 20:19,26). In any event, it seems that the first day of the week probably came to be known as the "Lord's Day" (Rev. 1:10), and seems to have been the day on which the church gathered with the approval of the Apostles (Acts 20:7).
There does not appear to be any evidence in the New Testament that the early church felt compelled to observe the seventh day of the week as the Sabbath, and there is some possible evidence that Paul taught that Christians were not obligated to observe that particular day (Col. 2:16).
In King James version: "Let no man therefore judge you in meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath days: Which are a shadow of things to come; but the body is of Christ
http://www.ellopos.net/elpenor/koinonia/topic.asp?TOPIC_ID=272
Conclusion..
In conclusion, the practice of Sunday observance is based first on the understanding that the Bible does not command observance on the seventh day of the calendar week, and second on church tradition established under the approval of the Apostles. and the change of the
use of the Calendar.
http://www.thirdmill.org/answers/answer.asp/file/99959.qna/category/th/page/questions/site/iiim