I'm jumping in here mid way with only reading the OP so far so here is my
There is no formula for God's salvation, but only His plan of salvation by, in the OT "faith" and in the NT "faith" as all who will believe will be saved.
1st Covenant promise OT
Gen 17:1 And when Abram was ninety years old and nine, the LORD appeared to Abram, and said unto him, I am the Almighty God; walk before me, and be thou perfect.
Gen 17:2 And I will make my covenant between me and thee, and will multiply thee exceedingly.
Gen 17:3 And Abram fell on his face: and God talked with him, saying,
Gen 17:4 As for me, behold, my covenant is with thee, and thou shalt be a father of many nations.
Gen 17:5 Neither shall thy name any more be called Abram, but thy name shall be Abraham; for a father of many nations have I made thee.
Gen 17:6 And I will make thee exceeding fruitful, and I will make nations of thee, and kings shall come out of thee.
Gen 17:7 And I will establish my covenant between me and thee and thy seed after thee in their generations for an everlasting covenant, to be a God unto thee, and to thy seed after thee.
Reiterated in NT
Heb 11:17 By faith Abraham, when he was tried, offered up Isaac: and he that had received the promises offered up his only begotten son,
Heb 11:18 Of whom it was said, That in Isaac shall thy seed be called:
Heb 11:19 Accounting that God was able to raise him up, even from the dead; from whence also he received him in a figure.
2nd New covenant of God's grace as Christ being God's plan of salvation before the foundation of the world
John 3:16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
Joh 3:17 For God sent not his Son into the world to condemn the world; but that the world through him might be saved.
Gal 3:26 For ye are all the children of God by faith in Christ Jesus.
Gal 3:27 For as many of you as have been baptized into Christ have put on Christ.
Gal 3:28 There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.
Gal 3:29
And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise.
OT or NT God's salvation has always been by faith in Him and His only begotten Son Christ Jesus as we are obedient to His commands.