A good study of the sabbath comes from the book of Hebrews.
Heb 4:4-11 For he spake in a certain place of the seventh day on this wise, And God did rest the seventh day from all his works. (5) And in this place again, If they shall enter into my rest. (6) Seeing therefore it remaineth that some must enter therein, and they to whom it was first preached entered not in because of unbelief: (7) Again, he limiteth a certain day, saying in David, To day, after so long a time; as it is said, To day if ye will hear his voice, harden not your hearts. (8) For if Jesus had given them rest, then would he not afterward have spoken of another day. (9) There remaineth therefore a rest to the people of God. (10) For he that is entered into his rest, he also hath ceased from his own works, as God did from his. (11) Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief.
The sabbath of the law was a picture of a reality that was ushered in by the sacrifice of Jesus Christ. For a born again believer the sabbath has nothing to do with a day of the week. I have heard many argue over the old testament sabbath and the new testament "Lord's day". Saturday? Sunday? Both are irrelevant.
Col 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: (17) Which are a shadow of things to come; but the body is of Christ.
Rom 14:5-6 One man esteemeth one day above another: another esteemeth every day alike. Let every man be fully persuaded in his own mind. (6) He that regardeth the day, regardeth it unto the Lord; and he that regardeth not the day, to the Lord he doth not regard it. He that eateth, eateth to the Lord, for he giveth God thanks; and he that eateth not, to the Lord he eateth not, and giveth God thanks.
The sabbath was a picture of resting from your own labors, your own works just as Christ did from His and is a resting and striving issue. We enter into the rest of Christ, the sabbath rest, when we cease from our own labors and instead walk by faith in what Jesus accomplished for us. It is a rest of faith and freedom from works. The original picture of this rest, the sabbath day of the law, was always about the obedience of faith.
Rom 16:25-26 Now to him that is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began, (26) But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith:
You see, the law held a mystery in the thing it was a shadow or picture of, and now that mystery is revealed to us. That mystery was the Gospel and the atoning work of Christ that brought us righteousness by grace through faith, not of works and law-keeping. The obedience we now have is one of faith, not of works. But the picture, the sabbath, both the day which Israel prided themselves in and the year which they never kept because of their unbelief that God could provide for them even through a year of allowing the land to rest.
Lev 26:32-35 And I will bring the land into desolation: and your enemies which dwell therein shall be astonished at it. (33) And I will scatter you among the heathen, and will draw out a sword after you: and your land shall be desolate, and your cities waste. (34) Then shall the land enjoy her sabbaths, as long as it lieth desolate, and ye be in your enemies' land; even then shall the land rest, and enjoy her sabbaths. (35) As long as it lieth desolate it shall rest; because it did not rest in your sabbaths, when ye dwelt upon it.
God judged the people of Israel for this lack of faith and the land experienced the sabbath years that Israel had lacked the faith to keep.
It is about a walk of faith, and it always has been. So for a new testament believer to wrangle over the day of the week is to miss,I believe, a very significant part of what the Gospel is all about.
Is it a good idea to take one day of seven to rest and to focus our attention on God? Absolutely. I am 100% for it and would advise it wholeheartedly, but not because believe it is commanded that I do so, but rather because it strengthens me both physically and spiritually. But the sabbath is about the rest of a walk of faith.