Therefore, to you who believe, [Jesus] is precious; but to those who are disobedient, “The stone which the builders rejected has become the chief cornerstone,” and “a stone of stumbling and a rock of offense.”
1 Peter 2:7–8 NKJV
Young's Literal Translation
1Pe 2:6 Wherefore, also, it is contained in the Writing: `
Lo, I lay in Zion a chief corner-stone, choice, precious, and he who is believing on him may not be put to shame;'
1Pe 2:7 to you, then, who are believing is the preciousness; and to the unbelieving [unpersuaded, not convinced], a stone that the builders disapproved of, this one did become for the head of a corner,
1Pe 2:8 and a stone of stumbling and a rock of offence--
who are stumbling at the word, being unbelieving, --to which also they were set;
What were they believing or not believing [not convinced of]?
Mar 8:29 And he saith to them, `And ye--who do ye say me to be?' and
Peter answering saith to him,
`Thou art the Christ.'
The long awaited Messiah, the Anointed One.
In verse 6 Peter quotes from the Writing, the Hebrew text....
Isa 28:16 Therefore, thus said the Lord Jehovah: `Lo, I am laying a foundation in Zion, A stone--a tried stone, a corner stone precious, a settled foundation,
He who is believing doth not make haste. [He will not avoid, run away from the truth].
So it really doesn't matter if G544 is translated as unbelieving or disobedience, it is talking about one particular disobedience that will surely cause a person to not be saved. Not obeying the Gospel, the truth of who Jesus was/is, the Christ.
2Co 5:20 in behalf of Christ, then, we are ambassadors, as if God were calling through us, we beseech, in behalf of Christ, `
Be ye reconciled to God;'
