Are Christians supposed to serve God only on Sunday, or every day of the week?
Believers are to serve God every day of the week. Scripture does not set Sunday above the other six days as a special holy day; Paul says regard every day alike. The believer's service belongs Monday through Friday just as much as Saturday and Sunday.
Les teaches that in this age of grace the book says nothing about practicing a system of worship; Christ nailed it to His cross, and believers are free. Paul in Romans 13 says not to regard one day higher than another but to regard every day alike. Les notes he has nothing against Sunday, but Sunday is not taught in Scripture as a special holy day above the other six. Paul mentioned the first day of the week for bringing offerings, but setting Sunday apart as uniquely holy is not taught. Every day is alike for the believer, so we serve God just as much Monday through Friday as Saturday and Sunday. Les then points to Galatians 4, where Paul wrote because Judaizers were convincing Gentiles they had to keep the Law for salvation; Paul admonished them not to become legalists, a temptation that remains today because people like to satisfy their ego with what they do, but God will have none of it.