Ellen G. White (1827-1915) and James White (1821-1881): Founders of Seventh-day Adventism [public domain / Wikimedia Commons]
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I was in a Facebook discussion with Seventh-day Adventists about their view that worship takes place properly on the Sabbath (Saturday) and not Sunday. I provided a link to a collection of links on the topic that I compiled, then made my own comments (and it became a mini-argument).
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wrote: Yes, people from different churches speak out against the Seventh-day Adventist Church because we believe in the Sabbath. But no one can give a Bible answer as to where in the Bible you find the truth about Sunday worship.
Moreover, nowhere in the Bible can you find that all spiritual truth has to come from the Bible and the Bible alone. You are therefore contradictory.
The most obvious reason the early Christians worshiped Sunday was because it was the day Jesus rose from the dead. Thus, it was a development of the Old Testament Sabbath, as were many Christian doctrines developed from the traditions of the Old Testament.
Sunday worship or as I sometimes say Sunday worship is not biblical. They say Christians take it as a day of worship because of Jesus. This is the question: How can you take it if God has not given it? Read the New Testament and you won’t find it.
Sunday worship is indeed mentioned:
Acts 20: 7 (RSV) On the first day of the week, when we were gathered to break bread, Paul spoke with them, intending to leave the next day; and he continued his speech until midnight. (cf. 20:11)
The breaking of bread is the worship service (Holy Communion). The “first day” is Sunday, as in the stories of the Resurrection (Mk 16: 2, 9; Lk 24: 1; Jn 20: 1). One of the appearances of the Resurrection of Jesus also took place on a Sunday (Jn 20:19).
We know that “breaking bread” is a Eucharistic term. This was the worship of the early Christians, and we know from Acts 20: 7 that it was Sunday, not Saturday, although at that time the apostles still simultaneously observed Jewish services in the synagogues and the temple. (because they remained practicing Jews; it was decided in the Council of Jerusalem [Acts 15] that pagan Christians – who will soon be the vast majority of all – do not need to keep all Jewish laws).
Other cases of “breaking the bread”:
Acts 2:42 And they dedicated themselves to the teaching and to the fellowship of the apostles, to the breaking of bread and to prayers.
Acts 2:46 And day after day, attending the temple together and breaking bread in their homes, they ate with a joyful and generous heart,
1 Corinthians 10: 16-17 The cup of blessing which we bless, is it not a participation in the blood of Christ? The bread which we break, is it not a participation in the body of Christ?  Because there is only one bread, we who are many, we form one body, because we all participate in the same bread.
This motif in turn refers to the expressions used at the Last Supper, which was a paschal dinner (Mt 26:26; Mk 14:22; Lk 22:19).
And this is repeated in the passage about the disciples on the road to Emmaus, who met the risen Jesus (Lk 24, 30, 35). This is repeated again in Paul’s Eucharistic formula (1 Cor 11:24).
Thus, we know without a doubt that the formula of the “breaking of the bread” referred to Christian worship. Acts 20: 7 places this on Sunday. And the apostle Paul was there, so we know he sanctioned it and Luke, who wrote the Acts under the inspiration of God, sanctioned it too, casually presenting it with approval.
It can also be argued that Paul was referring to gathering together to worship on Sunday in the following passage, as it made sense that when a church was gathered to worship, it would be time to fundraise, as we are doing now, in passage of the plate:
1 Corinthians 16: 1-2 Now concerning the contribution for the saints: as I have led the churches in Galatia, you too must do this.  On the first day of each week each of you is to put something aside and store it, as it may prosper, so that contributions do not need to be made when I come.
It is never recorded in the New Testament that Christians gathered to worship or “break bread” on the Sabbath (Saturday).
But you told me I wouldn’t “find” that in the NT. Wrong!
For an in-depth article that delves into much more than that, including answers to many SDA arguments, see “Should we keep the Sabbath? “ by James A. Borland (Christian Research Journal, Volume 26, Number 2, 2003).
But I found my arguments just by looking at the NT and doing word searches. It was easy to reject your request.