God established the seventh day (Sabbath) as a day of rest after the six days of creation (Genesis 2:3). This day was not just given to the Jews, it was given previously to Adam and his children. Therefore it can be said that all people of faith should keep the Sabbath. Many Christians keep the Sabbath but this doesn't restrict them from also coming together in a formal worship on Sunday the first day of the week. A personal relationship with God has nothing to do with a religion or a denomination, so you are free to worship on the Sabbath and at the same time, if you desire, come to church on Sunday and fellowship with other Christians. The truth of the matter is every day of the week belongs to God and our worship of Him should be reflected in our daily walk.
The Law was intended to show us our need for Christ in that not one soul could keep it perfectly. The Law was intended to bring us to Christ! Gal 3:24-26 "Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith. But after that faith is come, we are no longer under a schoolmaster. For ye are all the children of God by faith in Christ Jesus."
Christians go to church on Sunday, the first day of the week, because it was the day of Christ's resurrection, and Pslam 118, which speaks to the day of Christ's resurrection, is a day to rejoice. Psa 118:24 "This is the day which the LORD hath made; we will rejoice and be glad in it." Christ as set you free to worship Him anytime you wish! John 8:32, 36 “And ye shall know the truth, and the truth shall make you free. If the Son therefore shall make you free, ye shall be free indeed.” And Paul tells us in Romans not to get hung up on ritual diets or holy days, Rom 14:5-8 “One man esteemeth one day above another: another esteemeth every day alike. Let every man be fully persuaded in his own mind. 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.For none of us liveth to himself, and no man dieth to himself. For whether we live, we live unto the Lord; and whether we die, we die unto the Lord: whether we live therefore, or die, we are the Lord's.”