The Biblical Sabbath, however, is and has always been on the seventh day of the week, or Saturday. Despite the prevalence of Sunday worship in Christendom, we must look to the Bible as our authority and keep the seventh day Sabbath ordained by God.
Remember Paul said; (Acts 24:14) “But this I confess unto thee, that after the way which they call heresy, so worship I the God of my fathers, believing all things which are written in the law and in the prophets:” And it says clearly in the law (Ex:20) to remember the sabbath, to keep it holy.
And yet, the Apostles were having meetings on the first day of the week which is Sunday... weird!
We see in Acts chapter 2 that the first church service was on Sunday (the day of Pentecost they were all with one accord in one place and received the outpouring of the Holy Ghost). And, the first public evangelism meeting was also held on Sunday out in the street after the Holy Ghost was poured out in the upper room (Acts 2:14-36)
Acts 20:7
The first day of the week, the Apostles came together to break bread
1 Corinthians 16:2
Upon the first day of the week let every one of you lay by him in store, as God hath prospered him
Colossians 2:16,17
Let no man therefore judge you in meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath days:
Which are a shadow of things to come; but the body is of Christ.
Why follow the shadow of things that were to come after Jesus has arrived where we can join Him in The feast of First Fruits? Let no man therefore judge you concerning not observing Saturday sabbath seeing it's not a requirement given in the New Testament for salvation!
The Lord instructed the Israelites, “You shall count seven weeks for yourself; begin to count the seven weeks from the time you begin to put the sickle to the grain” (Deuteronomy 16:9). The word Pentecost means fifty, and it comes fifty days from the feast of First Fruits (Leviticus 23:10–11, 15–17). The feast of First Fruits was to occur on the day after the Sabbath (verse 11), which was always the Sunday of Passover week. Pentecost, then, was the day after the seventh following Sabbath (verses 15–16), which would be the fiftieth day after First Fruits and also falls on a Sunday.
Jesus died on the Friday of Passover week and had to be buried hastily before sunset, which was when the Sabbath began. His body remained in the sepulcher throughout the Sabbath day, but on that Sunday morning, when the priest was to offer the First Fruits offering in the Temple, Christ arose from the dead as the first fruits of them that slept (I Corinthians 15:20).
For forty days, Jesus appeared to His disciples and then ascended into Heaven. Ten days later, the Sunday of the Feast of Pentecost, the Holy Spirit descended upon the believers in Jerusalem. The only biblical reference to the events of Pentecost is Acts 2:1-3. At Pentecost, the disciples witnessed the birth of the New Testament church in the coming of the Holy Spirit.
The evidence shows that the First Fruits and Pentecost were always intended to fall on Sundays, without regard to the day of the month they occurred. As for the New Testament record, it is clear that Jesus arose from the dead on Sunday, the First Day of the Week, the day after the Sabbath, as the fulfillment of the feast of First Fruits. These dates were the literal fulfillment of the Old Testament feasts verifying the powerful meaning of the death and resurrection of Christ.
Jesus is the first fruits, or first born among many brethren
Romans 8:29
For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
God's Word teaches the old covenant has been done away with because we now have a NEW covenant
Hebrews 10:9
Then said he, Lo, I come to do thy will, O God. He taketh away the first, that he may establish the second.
God's Word teaches that Christians are NOT following Moses as their high priest because now we have a NEW High Priest Who is Jesus Christ?
Hebrews 7:12
For the priesthood being changed, there is made of necessity a change also of the law.
God did away with the old covenant where Moses was the high priest and made a new Covenant where Jesus Christ is the High Priest and since the priesthood has been changed, there has been a change of the law from the law of Moses to the Law of Christ..
Galatians 5:4
Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.
Those who try to keep the law of Moses are responsible for keeping ALL of the law of Moses and if they don’t keep all of the law, they are guilty of failing to keep the law. Christians are NOT called to keep the law of Moses... we are under the law of Christ now. (see - Galatians 6:2, 1 Corinthians 9:21, James 2:12, James 1:25, Romans 8:2, 2 Peter 1:4-10)
James 2:10
For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all.
Hebrews 3:1-6
Wherefore, holy brethren, partakers of the heavenly calling, consider the Apostle and High Priest of our profession, Christ Jesus;
Who was faithful to him that appointed him, as also Moses was faithful in all his house.
For this man was counted worthy of more glory than Moses, inasmuch as he who hath builded the house hath more honour than the house.
For every house is builded by some man; but he that built all things is God.
And Moses verily was faithful in all his house, as a servant, for a testimony of those things which were to be spoken after;
But Christ as a son over his own house; whose house are we, if we hold fast the confidence and the rejoicing of the hope firm unto the end.
You can have church on Saturday if you want to... but it's crossing the line to tell others they are in sin if they don't observe Saturday sabbath seeing there is no such command or teaching from Jesus or His Apostles saying Christians are required to observe Saturday sabbath under the New Covenant.