And coming to Him as to a living stone which has been rejected by men, but is choice and precious in the sight of God,you also, as living stones, are being built up as a spiritual house for a holy priesthood, to offer up spiritual sacrifices acceptable to God through Jesus Christ. For this is contained in Scripture: “BEHOLD, I LAY IN ZION A CHOICE STONE, A PRECIOUS CORNER stone, AND HE WHO BELIEVES IN HIM WILL NOT BE DISAPPOINTED.”This precious value, then, is for you who believe; but for those who disbelieve, “THE STONE WHICH THE BUILDERS REJECTED, THIS BECAME THE VERY CORNER stone,” and, “A STONE OF STUMBLING AND A ROCK OF OFFENSE”; for they stumble because they are disobedient to the word, and to this doom they were also appointed. (1 Peter 2:4–8)
"In Ps. 117 LXX the rejected stone has become the chief cornerstone of God’s building program. ... Even in the psalm, the chief cornerstone rejected by “the builders” is closely associated with salvation, implying that to reject the stone is to jeopardize one’s salvation. Alluding to the later Greek versions of Isa. 8:14, Peter further describes the stone in relation to those who reject it as a stone of stumbling (προσκόμματος, proskommatos) and a rock of temptation to sin (σκανδάλου, skandalou, 2:8).4 Ironically, Peter himself (the rock) was accused by Jesus of being a skandalon when Peter rebuked Jesus and attempted to deflect him from his predicted road to rejection and death (Matt. 16:23). Peter had become an occasion for Jesus to sin, a temptation that Jesus vigorously overcame by his sharp rebuke of Peter’s thought. Here in 1 Pet. 2:8 Peter claims that Christ the cornerstone presents an opportunity either for trust or for rejection. Moreover, rejection of Christ is not an amoral decision; it is itself an instance of sin. This is a message that our religiously pluralistic society today finds just as offensive as did first-century polytheistic society. To reject Christ is to stumble and sin. (ed., bold added) Peter quotes only the portion of Isa. 8 that refers to those who reject and stumble, but that passage also refers to the rock as a refuge for those who trust (Isa. 8:13–14 LXX): “Sanctify the Lord himself; and he himself will be your fear. If you trust in him, he will become your sanctuary, and you will not encounter him as a stumbling caused by a stone, nor as a fall caused by a rock” (NETS). Isaiah is speaking of those who do trust in the Lord. Peter uses the prophet’s words to reflect on those who do not. By implication, those who have not trusted in the Lord have not “sanctified” him, and therefore they have indeed encountered him as a stone and rock over which they have fallen.
As Marshall (1991: 73) summarizes, the quotation of Isa. 28:16 LXX and Ps. 117:22 LXX (118:22 Eng.) functions in Peter’s argument first to explain that the unbelief of those who reject Christ was already predicted in the OT prophecies; therefore, the rejection of Christ by friends and neighbors should not cause Christians surprise or doubt in their own faith. (ed., bold added)Second, Peter has clearly presented Jesus Christ as the only means of salvation, by which all will be judged. When people reject him, they do it to their own peril." (Jobes, K. H. 1 Peter (Baker Exegetical Commentary on the New Testament). Baker Academic, 153-154)