The vast majority of Christians around the world observe Sunday as their day of worship-many doing so in honor of Christ's resurrection. However, there is no biblical foundation for this widespread practice. Names for the days of the week are not used in the Bible, with the exception of Sabbath for the seventh day of the week. Sunday is referred to as the "first day" of the week.
So what does the New Testament actually say about Sunday, the "first day" of the week? Well, not much. Let's take a look …
1. — The Gospels: Each Gospel records Christ's death and identifies His resurrection as occurring on the "first day of the week." (See Matthew 28:1; Mark 16:1-3, 9; Luke 24:1, 2; John 20:1.) While some theologians disagree about what day Christ died, Luke is clear that the women preparing spices for Christ's body "rested on the Sabbath according to the commandment" (Luke 23:56).
2. — John 20:19: "The same day at evening, being the first day of the week, when the doors were shut where the disciples were assembled, for fear of the Jews." This verse describes a meeting of the disciples after Christ's resurrection. However, according to the text, they met out of fear-not for the purpose of worship.
3. — Acts 20:7: "On the first day of the week, when the disciples came together to break bread, Paul, ready to depart the next day, spoke to them and continued his message until midnight." While the Scripture indicates a gathering of likeminded believers held on the first day of the week, scholars recognize that this meeting took place in the evening, our Saturday night, and lasted until midnight.
4. — 1 Corinthians 16:1, 2: "Concerning the collection for the saints, … On the first day of the week let each one of you lay something aside, storing up as he may prosper, that there be no collections when I come." The apostle Paul is giving final instructions regarding a goodwill offering he is planning to take to Jerusalem; there is no mention of worship in the text or the surrounding context.
Many sincere Christians have not considered these passages and that Sunday wasn't seen as a holy day in the lives of early believers;
click here for a great resource that delves deeper into the problems of Sunday worship.