The answer to this question is self evident to those living under the "law of grace", but to those living outside of grace, they seek to quote "chapter and verse" and require everyone else to live according to their interpretation of same. The Jews asked Jesus, "where should we worship?" His reply, "True worshipers worship the Father in spirit and in truth". The question which is posed above seeks a "legal" answer along with a justification for that answer. Jesus' life and death was not to establish another religion for people to "follow" according rules, regulations and special days, weeks, months, celebrations, etc., but to free us all from the dictates of religious traditions so that we can live according to God's word as revealed within us, free from the law, free from guilt, free from sin. And, no, my response does not encourage license to "do anything". Being a Christian requires that we live according to the law of love, and grace, and forgiveness. Who among us would not want to be with others who share this beautiful truth, only without a mandate that we MUST do so on a certain day of the week, or with a certain group of people other than those who have found this same truth, this same freedom, this same love?
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I think this answer is one of the best in the threads.
No, we don't have to do anything on a certain day. We Born-Again Christians have two laws: Love God more than anything, and Love everybody else as much as we love ourselves.
If you do these two things, everything else falls into place with the help of the Holy Spirit. If you love God, you love Jesus (He says many times in the Gospels that 'he who loves the Father loves Me' and he tells the Pharisees that 'since you don't believe in Me, then you don't believe in He who sent me' and many other things He said along these lines).
If you love Jesus, then you will do what He instructs you to do through the Holy Spirit. You will seek His guidance, His wisdom, His will for you. You will want to read His word, you will want to hear Him through the Scriptures, and you will want to be around others who are in Him.
All of these things come with Loving Christ (and of course, through Him, the Father also).
So anybody that tells you that you must do this, or you must do that, is only trying to attach rules, regulations, rituals, days, moons, all of the things the Bible says we ought to be freed from.
In fact, the Bible (Paul) says that Colossians 2:16, that "Let no man judge you in meat, drink, or in respect of an holyday, or of the new moon, or of the sabbath days".
This includes both Saturday AND Sunday.