Dear Collin:

The first thing to remember is that the word "sabbath" does not mean "Saturday." Our English word "Sabbath" comes from the  Latin sabbatum,Greek sábbaton, and the Hebrew shabbâth, all of which means "rest." It is Jewish tradition, not Scripture, that considered Saturday to be the "seventh" day and who set the day of rest on Saturday. The days mentioned in the Genesis narrative of creation (Genesis 2:1-3) are not given names, nor do the Ten Commandments (Exodus 20:8–11) give the name of the day of the Sabbath. This was all determined by tradition.

The Seventh Day Adventists rather humorously say that Sunday cannot be the day of rest because Sunday was named by the pagan Romans honoring the "Day of the Sun." [Danny Shelton and Shelley Quinn, Ten Commandments Twice Removed (Coldwater, MI: Remnant Publications, Inc., 2006), 76-77]. 

Every day of the week is named after some pagan god. Saturday is dies Saturni, "Saturn's Day", named by the ancient Romans in honor of Saturn. So if the Sabbath cannot be on a day named after a pagan god, the Sabbath cannot exist at all. Such silliness.

The Seventh Day Adventists also claim the is not a single verse in the Bible referring to Christan Sunday "sabbath." They must be blind because Acts 20:7 proves weekly communion on Sunday (1st Day) and 1 Corinthians 16:1-2 proves weekly church collection on Sunday (1st Day). Also see Colossians 2:16-17 and Revelation 1:10. It is clear that the first century Christians were not bound to the Jewish Sabbath (how could they be after Gentiles, who are not bound by Jewish traditions, began converting to Christianity), and instead worshiped on Sunday, in honor of the Day of the Resurrection. This is proved by the Council of Jerusalem around A.D. 50.

The Council's Apostolic Decree, concluded that most of the Mosaic law did not bind the Gentiles, including the requirement for circumcision of males. Thus, this early Council help to differentiate the Christian Church from its Jewish roots.

For more on this, including quotations from the Church Fathers see the Catholic Answers article, Sabbath or Sunday?

We also need to remember that God gave the Church the authority to make decisions like this (e.g. "keys to the kingdom" Matthew 16:19).

God Bless,
Bro. Ignatius Mary