Saturday or Sunday Worship -- It Doesn't Matter what Day.
key verse Romans 14:5


A NT example of Sunday worship.
 

AC 20:7 On the first day of the week we came together to break bread. Paul spoke to the people and, because he intended to leave the next day, kept on talking until midnight. 8 There were many lamps in the upstairs room where we were meeting. 9 Seated in a window was a young man named Eutychus, who was sinking into a deep sleep as Paul talked on and on. When he was sound asleep, he fell to the ground from the third story and was picked up dead. 10 Paul went down, threw himself on the young man and put his arms around him. "Don't be alarmed," he said. "He's alive!" 11 Then he went upstairs again and broke bread and ate. After talking until daylight, he left. 12 The people took the young man home alive and were greatly comforted.


A NT example of a Sunday meeting (worship?)
 

1CO 16:1 Now about the collection for God's people: Do what I told the Galatian churches to do. 2 On the first day of every week, each one of you should set aside a sum of money in keeping with his income, saving it up, so that when I come no collections will have to be made. 3 Then, when I arrive, I will give letters of introduction to the men you approve and send them with your gift to Jerusalem. 4 If it seems advisable for me to go also, they will accompany me.


OT law to serve God's people for a time
 

GAL 4:1 What I am saying is that as long as the heir is a child, he is no different from a slave, although he owns the whole estate. 2 He is subject to guardians and trustees until the time set by his father. 3 So also, when we were children, we were in slavery under the basic principles of the world. 4 But when the time had fully come, God sent his Son, born of a woman, born under law, 5 to redeem those under law, that we might receive the full rights of sons. 6 Because you are sons, God sent the Spirit of his Son into our hearts, the Spirit who calls out, "Abba,* Father." 7 So you are no longer a slave, but a son; and since you are a son, God has made you also an heir.


Observation of "special days" an old enslavement
 

    GAL 4:8 Formerly, when you did not know God, you were slaves to those who by nature are not gods. 9 But now that you know God--or rather are known by God--how is it that you are turning back to those weak and miserable principles? Do you wish to be enslaved by them all over again? 10 You are observing special days and months and seasons and years! 11 I fear for you, that somehow I have wasted my efforts on you.


Become like me - resist the Judiazers

 GAL 4:12 I plead with you, brothers, become like me, for I became like you. You have done me no wrong. 13 As you know, it was because of an illness that I first preached the gospel to you. 14 Even though my illness was a trial to you, you did not treat me with contempt or scorn. Instead, you welcomed me as if I were an angel of God, as if I were Christ Jesus himself. 15 What has happened to all your joy? I can testify that, if you could have done so, you would have torn out your eyes and given them to me. 16 Have I now become your enemy by telling you the truth?


We are free and not under the old covenant commands (when fulfilled in Christ)
 

GAL 4:21 Tell me, you who want to be under the law, are you not aware of what the law says? 22 For it is written that Abraham had two sons, one by the slave woman and the other by the free woman. 23 His son by the slave woman was born in the ordinary way; but his son by the free woman was born as the result of a promise.

GAL 4:24 These things may be taken figuratively, for the women represent two covenants. One covenant is from Mount Sinai and bears children who are to be slaves: This is Hagar. 25 Now Hagar stands for Mount Sinai in Arabia and corresponds to the present city of Jerusalem, because she is in slavery with her children. 26 But the Jerusalem that is above is free, and she is our mother.


Rules of the Old Covenant, "written code" now "canceled"
 

COL 2:13 When you were dead in your sins and in the uncircumcision of your sinful nature,* God made you* alive with Christ. He forgave us all our sins, 14 having canceled the written code, with its regulations, that was against us and that stood opposed to us; he took it away, nailing it to the cross. 15 And having disarmed the powers and authorities, he made a public spectacle of them, triumphing over them by the cross.*


Don't let others judge you "with regard to" "a Sabbath day"
Sabbath day - "a shadow of things to come" that is things found "in Christ" i.e., "Lord's Day"
 

COL 2:16 Therefore do not let anyone judge you by what you eat or drink, or with regard to a religious festival, a New Moon celebration or a Sabbath day. 17 These are a shadow of the things that were to come; the reality, however, is found in Christ. 18 Do not let anyone who delights in false humility and the worship of angels disqualify you for the prize. Such a person goes into great detail about what he has seen, and his unspiritual mind puffs him up with idle notions. 19 He has lost connection with the Head, from whom the whole body, supported and held together by its ligaments and sinews, grows as God causes it to grow.


We should not argue about "disputable matters"
 

RO 14:1 Accept him whose faith is weak, without passing judgment on disputable matters. 2 One man's faith allows him to eat everything, but another man, whose faith is weak, eats only vegetables. 3 The man who eats everything must not look down on him who does not, and the man who does not eat everything must not condemn the man who does, for God has accepted him. 4 Who are you to judge someone else's servant? To his own master he stands or falls. And he will stand, for the Lord is able to make him stand.


An example of a "disputable matter" -- "one day more sacred than another"
 

RO 14:5 One man considers one day more sacred than another; another man considers every day alike. Each one should be fully convinced in his own mind. 6 He who regards one day as special, does so to the Lord. He who eats meat, eats to the Lord, for he gives thanks to God; and he who abstains, does so to the Lord and gives thanks to God. 7 For none of us lives to himself alone and none of us dies to himself alone. 8 If we live, we live to the Lord; and if we die, we die to the Lord. So, whether we live or die, we belong to the Lord.
RO 14:9 For this very reason, Christ died and returned to life so that he might be the Lord of both the dead and the living. 10 You, then, why do you judge your brother? Or why do you look down on your brother? For we will all stand before God's judgment seat. 11 It is written:

" `As surely as I live,' says the Lord,
`every knee will bow before me;
 every tongue will confess to God.' "*

RO 14:12 So then, each of us will give an account of himself to God.

RO 14:13 Therefore let us stop passing judgment on one another.


Personal Worship on "the Lord's Day"
 

Rev. 1:10 On the Lord's Day I was in the Spirit, and I heard behind me a loud voice like a trumpet, 11 which said: "Write on a scroll what you see and send it to the seven churches: to Ephesus, Smyrna, Pergamum, Thyatira, Sardis, Philadelphia and Laodicea."
Was the Sabbath in a sense revolked?
 
Hebrews 4:3 And yet his work has been finished since the creation of the world. 4 For somewhere he has spoken about the seventh day in these words: "And on the seventh day God rested from all his work."* 5 And again in the passage above he says, "They shall never enter my rest."

HEB 4:6 It still remains that some will enter that rest, and those who formerly had the gospel preached to them did not go in, because of their disobedience. 7 Therefore God again set a certain day, calling it Today, when a long time later he spoke through David, as was said before:

 "Today, if you hear his voice,
 do not harden your hearts."*


Is the other day of rest -- "the Lord's day"?
 

HEB 4:8 For if Joshua had given them rest, God would not have spoken later about another day.
 
Early Christian example of "Lord's day", Sunday worship

Didache 14.1
--"The Didache," an early Christian text written between 65 and 80 AD that was used as a
guidebook for the early Church.
 

14:1 But on the Lord's day, after that ye have assembled together, break bread and give thanks, having in addition confessed your sins, that your sacrifice may be pure.

14:2 But let not any one who hath a quarrel with his companion join with you, until they be reconciled, that your sacrifice may not be polluted,

14:3 for it is that which is spoken of by the Lord. In every place and time offer unto me a pure sacrifice, for I am a great King, saith the Lord, and my name is wonderful among the Gentiles.


http://www.ocf.org/OrthodoxPage/reading/St.Pachomius/Liturgical/didache.html

Another example of early Christian worship on Sunday

Justin, First Apology 67.3
--A biography of the Christian philosopher and apologist who was martyred in Rome in 165 AD.

http://www.ccel.org/fathers/ANF-01/just/justap1index.html
 

CHAP. LXVII.--WEEKLY WORSHIP OF THE CHRISTIANS.

And we afterwards continually remind each other of these things. And the wealthy among us help the needy; and we always keep together; and for all things wherewith we are supplied, we bless the Maker of all through His Son Jesus Christ, and through the Holy Ghost. And on the day called Sunday,(1) all who live in cities or in the country gather together to one place, and the memoirs of the apostles or the writings of the prophets are read, as long as time permits; then, when the reader has ceased, the president verbally instructs, and exhorts to the imitation of these good things. Then we all rise together and pray, and, as we before said, when our prayer is ended, bread and wine and water are brought, and the president in like manner offers prayers and thanksgivings, according to his ability,(2) and the people assent, saying Amen; and there is a distribution to each, and a participation of that over which thanks have been given,(3) and to those who are absent a portion is sent by the deacons. And they who are well to do, and willing, give what each thinks fit; and what is collected is deposited with the president, who succours the orphans and widows and those who, through sickness or any other cause, are in want, and those who are in bonds and the strangers sojourning among us, and in a word takes care of all who are in need. But Sunday is the day on which we all hold our common assembly, because it is the first day on which God, having wrought a change in the darkness and matter, made the world; and Jesus Christ our Saviour on the same day rose from the dead. For He was crucified on the day before that of Saturn (Saturday); and on the day after that of Saturn, which is the day of the Sun, having appeared to His apostles and disciples, He taught them these things, which we have submitted to you also for your consideration.


S. Bacchiocchi, From Sabbath to Sunday: An Historical Investigation of the Rise of Sunday Observance in Early Christianity, 1977.
JD Douglas (ed.), New Bible Dictionary. 2nd Edition. Tyndale, 1982.