Contrary to what your SDA friends what to think, “Sabbath keeping” has simply never been an issue or practice in the Christian East.
If they think there are such things as “Eastern Christian Sabbath Keepers”, they simply don’t know whereof they speak.
Consider this hymn from Holy Saturday Matins and Vesperal Divine Liturgy:
Great Moses mystically prefigured this present day when he said, ‘And God blessed the seventh day’. For this is the blessed Sabbath; this is the day of rest on which the only-begotten Son of God rested from all his works, through the dispensation in accordance with death, he kept the Sabbath in the flesh; and returning once again to what he was through the Resurrection he has granted us eternal life, for he alone is good and loves mankind.
As we can see, the sabbath commandment was a prophecy of Christ’s rest in the tomb.
Since the fulfilment of this figure and commandment, it has therefore passed away.
I might point out that SDAs themselves do NOT keep the sabbath at all. The particulars of sabbath observance in the Bible forbade lighting of fires–yet they drive their cars to church on the sabbath, and the internal combustion engine lights hundreds of fires a minute.
And as I’ve said, it was about REST FROM LABOR, not worship.
BTW, where did you get this tidbit in your original posting:
For example, it is said that John, the beloved, observed the sabbath and taught all christians to do so… it is known that he founded churches in asia, or the east.
It’s said by WHOM?
There is no such reference to this in the hagiographical tradition, and it’s quite extensive.
To paraphrase St. Paul, we have no such tradition, nor do the other Churches of God.