The Most Widely Accepted Error In Modern Christianity is going to church on sunday ...that sunday is the sabbath day ... For over 1,600 years the majority of the Christian world has been taught, and has accepted without question, that Sunday is the Christian's day of worship. Yet the Scriptures, historical records, and direct quotations from every major Christian denomination, all agree that this commonly taught belief is a blatant error.....
The truth is that God's Sabbath day has always been the seventh day of the week-(which today is called) Saturday.
Upon checking the common Gregorian calendar [with the exception of some calendars which are numbered for banking or accounting purposes], you will find, looking from left to right, that Sunday is the first day of the week, followed in order by [second] Monday, [third] Tuesday, [fourth] Wednesday, [fifth] Thursday, [sixth] Friday, and [seventh] Saturday. Saturday is the seventh day of the week in our modern world wide culture. If you have an opportunity to check older calendars, dating back as far as you can find, even from other countries, you will find the same relationship between Saturday and Sunday. Sunday is the first day of the week, and Saturday is the seventh day of the week. Further, it has been established that this seven-day weekly cycle has never been disrupted or broken, even back to the time of Adam and Eve.
Worshipping on Sunday goes back at least two thousand years before Jesus Christ. Shortly after the flood in Noah's time, Nimrod and his mother-wife, Semiramis, founded the great pagan religions. Sun worship is related to fire worship. From the beginning at the Tower of Babel, sun worship spread throughout the ancient world...
Historically, pagan Babylon worshipped the sun as a deity, and pagan religions also worshipped the invincible sun. The pagan ideas crept into the early church and with the assistance of Constantine, his civil Sunday law transferred the Sabbath rest to the Sun Day, and filled the church with commonly used pagan images and symbols of the sun.......ironically, Satan by deluding man into keeping the fiery pagan day of the Sun -- SUNDAY -- causes man to commemorate something else than what God set forth.......
In fact, the names for the days of the week came from pagan Gods or worship. Sun–day was named after the sun. Moon-day named from the worship of the moon became Monday. From the worship of the pagan god Tiu came Tiu’s-day or Tuesday. From the pagan god Woden came Woden’s-day or as we know it today Wednesday. Thor’s-day became Thursday. Frigga’s-day became Friday, and Saturn-day became Saturday...
In the Bible the only day that had a name recognized was the seventh-day Sabbath. Sunday was simply called in the Bible “the first day of the week.”(See John 20:1). So the false religion of sun worship in Isreal was Baal, its very clear and though other names were used in different languages, it all came from the same source, and God clearly says to come out of that false religion, whose source is 'Babylon'.... To me God is not a Sunday thing ..its an every day thing ..

Nice write up Nina4u. Some things were interesting but how did you know this

"Further, it has been established that this seven-day weekly cycle has never been disrupted or broken, even back to the time of Adam and Eve. "

The Gregorian was introduced to mark time based on the revolution of the earth, highly influenced by the Roman church. So how did you know that our Thursday which is our (depends) fifth day of the week is still the same thursday and fifth day of the week when you go back in time to 19 B.C?

How did you that the first day the biblical God started creation was on a Sunday and actually rested on a Saturday??

Do you know that Monday is the first day of the week according to International standard, ISO 8601?
Various Christians have their reasons for worshiping on a Sunday and other days they chose.