There is some debate going on pertaining to the day of rest, that is, the Sabbath. The Jews keep Saturday so why do we keep Sunday?
Your question comes up constantly today and I think my answer will be different from what you may have heard. I am going to tell you what has satisfied me with regard to this issue:
1. The Sabbath has never changed. It is still the seventh day and it is still Saturday.
2. Some say that we keep the ten commandments as Christians. Now nine of the ten are brought into the new testament as moral truth for our day. As a matter of fact the requirements of grace are higher than that of law, for example, killing becomes hate (See 1 John 3:15, Whosoever hateth his brother is a murderer: and ye know that no murderer hath eternal life abiding in him.) However, we are not under the law and when we say that we keep the ten commandments, we give ourselves a problem with the one requiring us to keep the Sabbath. The Lord kept the Sabbath, but not as the Jewish tradition required since they had added extra Biblical regulations, but He kept it as He Himself designed it. In Acts 15, the Gentiles were admonished to keep four things from the Jewish law and tradition (v 29 That ye abstain from meats offered to idols, and from blood, and from things strangled, and from fornication: from which if ye keep yourselves, ye shall do well.) Keeping the seventh day or Saturday was not one of the things mentioned. So as Christians we are not bound by the Sabbath.
3. New testament teaching concerning the Sabbath is that when we believe we enter into the Sabbath rest of God (Hebrews 4:3-4). So the old testament Sabbath is an illustration of new testament truth but we have to let the new testament explain the Sabbath for us.
4. Now why do we "keep the Sabbath" on the Lord's Day or the First Day of the Week? I personally do not. I think that the Lord has given us a principle that we should dedicate a day to Him and it should be a day of rest. None of us actually keeps the Sabbath on Sunday since we cook, buy gas, go to restaurants all of which would be prohibited under the Sabbath rules of the Old Testament. But because the Lord was raised from the dead on the first Day of the week, that day seems to be the day that early Christians used to remember Him and worship Him (See Acts 20:7, 1 Corinthians 16:2). The Sabbath is still Saturday and Sunday is the first day of the week or the resurrection day and is the day Christians use to worship corporately, and they dedicate this day to the Lord. We do not put new wine in old bottles (Matthew 9:17), that is we don't worship in this dispensation using the rules of the old dispensation which didn't work for the Jews and won't work for us. So I personally try to give Sunday to the Lord, but I do not consider myself to be keeping the Sabbath when I do.