Jesus said:
Joh 14:15 If ye love me, keep my commandments.
He was directly citing the OT, where He also said right in the Ten Commandments:
Exo 20:6 And shewing mercy unto thousands of them that love me, and keep my commandments.
What manmade 'creeds' say is / are irrelevant to what Jesus said, and irrelevant to what the OT-NT says.
The Early Church writings, are the NT, since Paul wrote 14 epistles thereof, and Peter wrote 2, John wrote 5 books, James/Jacob and Jude wrote theirs and Luke wrote 2, and Matthew & Mark wrote theirs.
I agree that the "teaching of the first church is quite obvious" since I (you, anyone) can read about it in the NT itself:
Mat. 12:1,2,5,8,10,11,12, 24:20, 28:1
Mar. 1:21, 2:23,24,27,28, 3:2,4, 6:2, 7:6-9, 15:42, 16:1
Luk. 4:16,31, 6:1,2,5,6,7,9, 13:10,14,15,16, 14:1,3,5, 23:54,56
Jhn. 5:9,10,16,18, 7:22,23, 9:14,16, 12:1 (calculated), 19:31
Act. 1:2, 4:24 (citing Exo. 20:11), 13:14,27,42,44, 14:15 (citing Exo. 20:11), 15:21, 16:13, 17:2, 18:4
Jhn. 12:1 (six days before the Passover, at Lazarus’ house)
Heb. 3:11, 4:1,3,4,5,8,9,10,11; [Heb. 4:9 “rest” Greek: sabbatismos, literal sabbath-keeping]
Rev. 1:10 [kuriake hemera, “the Lord’s Day” [the 7th Day Sabbath], see Gen. 2:1-3; Exo. 20:8-11; Deu. 5:12:15; Isa. 58:13, 66:23; Mat. 12:8; Mar. 2:27,28; Luk. 6:5; Rev. 10:6, 14:7,12]
Rev. 10:6 [see also Exo. 20:11, 31:17; Neh. 9:6; Psa. 146:6; Act. 4:24, 14:15, Rev. 14:7,12];
Rev. 14:7,12 [see also Exo. 20:11, 31:17; Neh. 9:6; Psa. 146:6; Act. 4:24, 14:15; Rev. 14:7,12].
Thus:
Jesus: (Luk. 4:16-19; Col. 1:16; Mar. 2:27; 1 Cor. 15:44-46)
Disciples: (Act. 1:2, (4:24), 13:14,27,42,44, (14:15), 15:21, 16:13, 17:2, 18:4; Heb. 3:11,18, 4:1,3,4,5,8,9,10,11;
Rev. 1:10, 10:6, 12:17, 14:6-7)
with us today: (Heb. 4:9; Rev. 1:10, 10:6, 12:17, 14:6-7; Jhn. 14:15; Exo. 20:6,8-11)
On into eternity: (Isa. 66:23)
Test: (1 Cor. 10:11; Exo. 16:1-36; Rev. 14:6-12)
I also document it here (Chapter 14, pages 186-361), in detail, in original language where available as well, along with actual documented Church History (which I did note, you did
not cite at all): -
The 7th Day The Sabbath - The Rest Of His Eternal Story (by Aaron Earnest) : Free Download, Borrow, and Streaming : Internet Archive
I think you should read those references again, and see all of the "Gentiles", who are keeping sabbath, and as scripture said:
Act 15:14 Simeon hath declared how God at the first did visit the Gentiles, to take out of them a people for his name.
Act 15:15 And to this agree the words of the prophets; as it is written,
Act 15:16 After this I will return, and will build again the tabernacle of David, which is fallen down; and I will build again the ruins thereof, and I will set it up:
Act 15:17 That the residue of men might seek after the Lord, and all the Gentiles, upon whom my name is called, saith the Lord, who doeth all these things.
Act 15:18 Known unto God are all his works from the beginning of the world.
Act 15:19 Wherefore my sentence is, that we trouble not them, which from among the Gentiles are turned to God:
Act 15:20 But that we write unto them, that they abstain from pollutions of idols, and from fornication, and from things strangled, and from blood.
Act 15:21 For Moses of old time hath in every city them that preach him, being read in the synagogues every sabbath day.
Notice, the Gentiles were repenting from violation of God's eternal laws, and keeping the sabbath of the LORD, holy, just as Prophecy said they would; Isa. 56:1,8; Jhn. 10:16; Isa. 56:2-7; &c.
Again, see all of the historical references I provide in the book as well. You are mistaken about the historical continuity of sabbath keeping among the Christian (Jews & Gentiles) communities.