Why does the first day of the week matter if Sunday was named after a pagan sun god?
The first day of the week matters because it was the day of the resurrection, not because of its pagan name. Even if pagans named it after the sun god, believers focus on the resurrection day. Paul directed the collection for the saints to be laid by on that same first day.
Les teaches that the first day of the week is significant because it was the resurrection day, not because of the pagan name attached to it. People had told him that Sunday was elevated as part of a pagan background, but he says he cannot help that pagans named the first day of the week, maybe after the sun god. The whole idea is not the name of the day but that it was the day of the resurrection. In 1 Corinthians 16, Paul gave order to the churches of Galatia that upon the first day of the week the collection for the Jerusalem saints was to be laid by in store. Les also notes this is not according to 10 percent, though that is a guideline seen when Abraham gave ten percent to Melchizedek; Paul says give as the Lord has prospered you, not under a mandate of law.