Holy Gospel of Jesus Christ according to Saint Luke 6:1-5.
While Jesus was going through a field of grain on a sabbath, his disciples were picking the heads of grain, rubbing them in their hands, and eating them.
Some Pharisees said, "Why are you doing what is unlawful on the sabbath?"
Jesus said to them in reply, "Have you not read what David did when he and those (who were) with him were hungry?
(How) he went into the house of God, took the bread of offering, which only the priests could lawfully eat, ate of it, and shared it with his companions."
Then he said to them, "The Son of Man is lord of the sabbath."
People nowadays seems no longer observe the Sabbath day. But usually, we are observing the Sabbath day as Sunday. However, is Sunday really the Sabbath day? We will not delves with the history on this matter. We must bear in mind that we don't have any calendar before. At the time of Jesus, calendar is not yet invented. When God created the universe, there was no calendar. So, the best thing we should do is always observed the Seventh day as the Sabbath day. So, anybody can set any day as Sabbath day. The important thing is you set at least a day in a week for the Lord.