God YHWH Who is a Spirit (John4:24) is the God of the 7th day Sabbath: Friday sundown till Saturday sundown:
"By the seventh day God finished the work that he had been doing, and he ceased on the seventh day all the work that he had been doing.
God blessed the seventh day and made it holy because on it he ceased all the work that he had been doing in creation", Genesis 2:2-3*.
"Remember the Sabbath day to set it apart as holy. For six days you may labor and do all your work,
but the seventh day is a Sabbath to the LORD your God; on it you shall not do any work, you, or your son, or your daughter, or your male servant, or your female servant, or your cattle, or the resident foreigner who is in your gates. For in six days the LORD made the heavens and the earth and the sea and all that is in them, and he rested on the seventh day; therefore the LORD blessed the Sabbath day* and set it apart as holy", Exodus 20:8-11
*Notice: this day only got God's special blessing!
Christ Yeshua (derrived "Jesus") is the Lord of the Sabbath:
"For the Son of Man is lord of the Sabbath", Matthew 12:8
So the one true God we worship is the God of the Sabbath. And Christ Yeshua, our Lord, is the Lord of the Sabbath.
Did God change? No, He is the Eternal God and He doesn't change. Did Christ change or change anything of his God? No, Christ didn't change and doesn't and cannot change anything God installed!
"So anyone who breaks one of the least of these Commands and teaches others to do so will be called least in the kingdom of heaven, but whoever obeys them and teaches others to do so will be called great in the kingdom of heaven", Matthew 5:19
The 7th day Sabbath is also the 4th Commandment of God (Exodus 20:8-11) and God ordains Christ and Christians (Revelation 1:1) to keep God's Commandments in Revelation 14:12:
"This requires the steadfast endurance of God's Elect— those who obey God’s Commandments and hold to their faith in Jesus".
The 7th day Sabbath is to be kept by all Christians. And that disciples/apostles broke the bread on the first day doesn't change God neither Christ. Moreover: they broke the bread on every day of the week, but only God's Sabbath received Special Blessings!
Church paganism is worship of the Babylonian trinity sungod Baalder, Easter and Tammuz with holy sun-day, holy Easter and holy winter solstice (= Xmas). Click here to read more: God calls His People out of Babylon
How the Bible was forged to fit church paganism for this trinity sungod from Babylon: Inserted forgeries in the Bible
More about God's Days & Feasts: God's feasts point to Gods plan