The seventh day of the week (now known as Saturday) is the holy Sabbath of God. It is the Lord’s Day.
Matthew 12:6-8 KJV
 But I say unto you, That in this place is one greater than the temple.  But if ye had known what this meaneth, I will have mercy, and not sacrifice, ye would not have condemned the guiltless.  For the Son of man is Lord even of the sabbath day.
Let that marinate.