It keeps getting repeated that "Sabbath is a shadow", as if that means it is to be dispensed with.
But is it?
Hebrews 8:4-5 KJV
For if he were on earth, he should not be a priest, seeing that there are priests that offer gifts according to the law: [5] Who serve unto the example and shadow of heavenly things, as Moses was admonished of God when he was about to make the tabernacle: for, See, saith he, that thou make all things according to the pattern shewed to thee in the mount.
The old covenant Levitical rites and priesthood were part of service to the shadow of heavenly things. That shadow is here specified to be the Tabernacle (and thus the temple, which was a more permanent phase of the tabernacle).
Hebrews 10:1-3 KJV
For the law having a shadow of good things to come, and not the very image of the things, can never with those sacrifices which they offered year by year continually make the comers thereunto perfect. [2] For then would they not have ceased to be offered? because that the worshippers once purged should have had no more conscience of sins. [3] But in those sacrifices there is a remembrance again made of sins every year.
Again, the law is said to have the shadow of good things to come. What law? The law of sacrifice and Levitical rites, the law of the Tabernacle (see ch 9 for more info). To leap from this to the 4th commandment is passe because it is a shadow requires an assumption, that whatever was in the law was a shadow. But that assumption would actually do away with all moral law whatsiever. So obviously that is not what Paul is discussing.
Colossians 2:16-17 KJV
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 : [17] Which are a shadow of things to come; but the body is of Christ.
This is recognised by exegetes as one of the hardest passages to translate, linguistically speaking. There are two options here.
1. The judging or criticism of the Colossian brethren by outsiders regarding the Colossians' eating, drinking, keeping holy day, new moons, and sabbath days. That criticism of liturgical practices was a shadow of things to come. Historically, this is dead on accurate. The rise of the apostasy which culminated in the creation of various sects (heresies) including catholicism included a vehement critique or judging and excommunication of Christians who practiced the original apostolic faith. The Lord's Supper was forbidden and replaced with a Mithraic "eucharist Mass", new holy days created, Sunday, etc etc.
2. Eating, drinking, holy day, new moons, and sabbath days are the shadow. If sabbath days are part of the shadow, so is eating and drinking. Eating does NOT refer to "kosher food law" of the old testament, that would be "food". But the Greek word is literally eatING. And it includdes drinking. There are no Mosaic stipulations about drinking except for Nazarites. So what is this eating and drinking? The Lord's Supper. The agape feast. The breaking of bread (communal fellowship meals).
In this case the Lord's Supper and the liturgical calendar practiced by the Christians are part of a shadow of coming things. We know the Lord's Supper is such (as long as ye eat this bread and drink this cup ye do show the Lord's death UNTIL HE COMES). So then what is being said is
apostolic Christian worship is a foretaste or shadow of things to come.
The Revelation details numerous acts of worship in the heavenly sanctuary which result in effects on earth according to the Divine Plan. Thus, worship follows a pattern or template that signifies the Divine Plan (prophecy). Prophecy and the outworking in earth of God's Plan is the enacting of WORSHIP AS IT OCCURS IN HEAVEN. The heavenly worship is a drama which depicts God's Plan for His creation. So when Christians worship (Biblically, that is) they are literally acting out the Divine prophetic plan of God in a representative fashion.
Either way you look at it, no indication arises that Sabbath keeping is obsolete.