Why do Protestants worship on Sunday? If the Sabbath is Saturday and it's known that the Roman Catholic Church changed the day week to worship from Saturday to Sunday, why then would Protestants continue to worship on Sunday?  I understand that Protestantism is a large group - I believe all of the sub-denominations do this for the same reason.  If there are different reasons per denomination, I'll either change the question or make a question for each Protestant Denomination.

Cardinal James Gibbons, The Faith of Our Fathers (Ayers Publishing, 1978)


  But you may read the Bible from Genesis to Revelation, and you will
  not find a single line authorizing the sanctification of Sunday. The
  Scriptures enforce the religious observance of Saturday, a day which
  we never sanctify.


John A. O'Brien, The Faith of Millions: the Credentials of the Catholic Religion Revised Edition (Our Sunday Visitor Publishing, 1974)


  But since Saturday, not Sunday, is specified in the Bible, isn't it
  curious that non-Catholics, who claim to take their religion directly
  from the Bible and not from the Church, observe Sunday instead of
  Saturday? Yes, of course, it is inconsistent; but this change was made
  about fifteen centuries before Protestantism was born, and by that
  time the custom was universally observed. They have continued the
  custom even though it rests upon the authority of the Catholic Church
  and not upon and explicit text in the Bible. That observance remains
  as a reminder of the Mother Church from which the non-Catholic sects
  broke away—like a boy running away from home but still carrying in his
  pocket a picture of his mother or a lock of her hair.
The choice of Sunday is traditional, but it is also harmonious with the Biblical account (emphasis added):


  Acts 20:7 NASB
  On the first day of the week, when we were gathered together to break bread, Paul began talking to them, intending to leave the next day, and he prolonged his message until midnight.
  
  1 Corinthians 16:2 (NASB)
  On the first day of every week each one of you is to put aside and save, as he may prosper, so that no collections be made when I come.
  
  Revelation 1:10 (NASB)
  I was in the Spirit on the Lord's day, and ...


There's a strong suggestion1 here that Sunday was day that the church met together. Because it was the day of Jesus' resurrection (Mt 28:1), it seems very sensible for the modern church to do this.

Also, bear in mind that there is no commandment from Jesus or the Biblical authors to worship or meet together on a particular day of the week. If one was not bound by the Law of Moses, why would it matter what day was chosen? Not all protestant groups believe that they are not bound, but of those who do, what compulsion would there be to worship on Saturday except for tradition and honor for the Jewish way?



1 In regards to the relevance and validity of including a passage about "the Lord's Day," I include the passage because is a possible example of Sunday having its own significance. It seems reasonable (though not the only conceivable reading) to understand this as Sunday because John used the word Sabbath nine times, never once referring to it as the Lord's day or giving it any other name. (The particular phrase doesn't appear anywhere else in the NT.) No other NT author referred to the Sabbath in any other way than the name already employed by the Jews. Revelation was presumably written later than his other writings, and so perhaps his understanding was better, or the phrase grew out of what was by that time established tradition (60-70 years after Jesus' death) of whatever day the Christians met together. To choose between the two most likely meanings, it seems to me that Sunday has a stronger case than Saturday.