Just because they claim to be Christian doesn't mean they are.
It is true that only Christ can judge the heart. But we can see people's fruits... and Paul had strong words against some people who weren't showing the fruits of being a Christian (and Paul is usually the grace poster child). And several people warn against wolves in sheep clothing.
JM
Christian = "follower of Christ"
Based on a strict interpretation of Matt 24:20, John 20:17
And especially...
Ezekiel 44:1-3,46:1-3
Would it be safe to say that worshippers on Sun-day (the day of the Sun) are
not following Christ?
Christ said He didn't come to abolish the law. Yet nearly every Christian(save SDA, 7th day Baptists, Messianics and a few other small groups) disobeys God in the name of Christ.
....and by such practice all call God a liar by not being able to count 3 days and 3 nights, since one clearly cannot fit such between Fri-Sun (while holding that He can count 40 days and 40 nights without problem)
Christ clearly said that those who do not believe that He is the Father(John 8:24) shall die in their sins.
The Father clearly and repeatedly says the Sabbath (Saturday) is His Day. It identifies Him.
99% of Christians say the next day is the "Lord's Day"
Yet God says He "does not change": Malachi 3:6
Numbers 19 gives a clear account of the sacrificial unblemished lamb. Christ says that :
Luke 24:44 44 ¶
And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me.
And yet I wonder how Christ fulfills this prophecy on "the first day of the week", when clearly the Numbers reference refers to the the 7th day (Numbers 19:19)
The fact is is that anyone can point to a sin of someone else and say "you're not a real Christian". I could point to a majority of persons who claim Christ and say "your not a real Christian" based on their SUN-day observance and they could look at my faults and say the same.