The adjective akrogōniaios is first attested in Greek literature in the Greek translation of Isaiah 28:16, where it describes a stone prophesied by Yahweh to be “the foundations of Sion.” The translator uses four adjectives to characterize this stone (lithon). It is “valuable (polutelē), choice (eklekton), ‘situated at the extreme angle’ (meaning given by Muraoka, A Greek-English Lexicon of the Septuagint, 23; similarly J. Lust, E. Eynikel, K. Hauspie a Greek-English Lexicon of the Septuagin I, 17; akrogōniaion), honoured (entimon).” M. Silva in “A New English Translation of the Septuagint” renders this as “a precious, choice stone, a highly valued cornerstone.” Silva interprets its function to be a substantival adjective meaning “cornerstone,” modified by the following adjective entimon (honoured).  The corresponding Hebrew text (the Masoretic tradition) speaks of “a stone, a testing or tested stone, a precious corner, establishing a foundation” (NRSV = “a foundation stone, a tested stone, a precious cornerstone, a sure foundation”). Understanding the intended meaning of the Hebrew text is difficult as the prophet piles up descriptors for this “stone.” The Septuagint translator seeks to replicate these multiple descriptors, more or less. akrogōniaion seems to represent the Hebrew noun pinnat that means “corner, corner-stone” (Koehler-Baumgartner, HALOT, 945. 1,3). It is part of a bound construction pinnat yiqrat, meaning “a corner stone regarded as precious/valued.” In the Isaiah text the stone probably is a metaphor for a person, a leader, whom Yahweh will use to bring salvation. “The one who puts confidence in it (stone)/him will never be ashamed/disappointed” (28:16c).

R. J. McKelvey in an article entitled “Christ the Cornerstone” (NTS 8, 352-9) argues that this term means “cornerstone, foundation stone,” contra Jeremias’ contention that it referred to a “copestone.” McKelvey concludes that in this compound term “akros…serves to intensify the force of gōniaios and accentuate the fact that the compound refers primarily to a stone at one or other of the ends or corners of the building” (354). It forms the corner of the foundation that “determined the ‘lie’ of the whole construction…” (355). He also notes that within the Qumran documents Isaiah 28:16 was used to demonstrate their view that they formed Yahweh’s spiritual temple and were its foundation, “that is the tested wall, the precious cornerstone” (1QS v.6).

This Isaiah text is quoted once in the New Testament (1 Peter 2:6) and perhaps alluded to by Paul in Ephesians 2:20. The writer of 1 Peter does not replicate the word order found in Septuagint Isa 28:16. In 1 Peter the text describes God placing in Sion “a stone (lithon), a cornerstone (akrogōniaion), chosen (eklekton), precious (entimon).” He uses it in the context of the metaphor that describes God’s construction of a “spiritual house,” made of “living stones.” The Lord Jesus is its “cornerstone” and God regards him as eklekton entimon (1 Peter 2:4). The writer’s reordering terms in the citation may reflect this earlier usage of these two adjectives. In Ephesians 2:20 Paul describes  Messiah Jesus as ontos akrogōniaiou “being the cornerstone” for the “holy temple” that God is building, composed of the followers of the Messiah and built upon the foundation of the apostles and prophets. These are the only contexts in which this term is used in the New Testament and both employ the extended metaphor of temple-building to describe God’s new action in forming the Messiah’s assembly. This linkage with foundations in OG Isaiah 28:16 and in the two New Testament references indicates that it does not refer to a capstone, but rather to a stone that anchors the foundation of a building in some way.

In 1 Peter 2, this citation is linked in the following verse (7) with Psalm 117:22 (118:22Heb). It may be that the writer intends the phrase eis kephalē gōnias “head of the corner” to function as definition for the rare term akrogōniaion that occurs in the citation from Isaiah (1 Peter 2:6). According to the author of Mark’s Gospel (12:10), Jesus referenced Psalm 117:22 to explain his rejection by the Jewish leaders and how this could be in fact the will of Yahweh. However, Jesus does not cite Isaiah 28:16 in any of his recorded sayings. Peter also refers to Psalm 117:22 in his speech before the Sanhedrin that Luke cites in Acts 4:11. In that context this citation becomes a metaphor of Jesus’ death and resurrection, the basis for human salvation.

In my opinion, the linkage of these two Old Testament texts (Isaiah 28:16 and Psalm 117:22) in 1 Peter 2 reveals that the early church leaders acknowledged Jesus’ self-reference as “head of the corner” because he employed the citation from Psalm 117:22. This encouraged them to consider other texts in the Jewish Scriptures where the metaphor of a stone that is the head of the corner/foundation might be understood in messianic terms. This brought Isaiah 28:16 to their attention. The use of the verb “put confidence in ” (pisteuō) in Isaiah 28.16c also encouraged this intertextual connection for the writer of 1 Peter. They may have been encouraged in this understanding by interpretations in Second Temple Judaism in which the stone image refers “to a mighty king” (Jobes, 1 Peter, 147).

Jeremias in his short article re akrogōniaios in the Theological Dictionary of the New Testament I. 792 claims that this term occurs in the Septuagint of 2 Kings 25:17 (OG 4 Kgdms 25:17). However, this is not correct according to the apparatus of the Cambridge Septuagint. In 2 Kings 25:17 this term occurs in the translation of Symmachus as the equivalent of the Old Greek’s rendering chōthar, a Greek transliteration of a Hebrew term referring to “the capital of a pillar” (Koehler-Baumgartner, HALOT 1, 507). Symmachus also used the term to translate “head of the corner” in Psalm 117.22 (McKelvey, 354). The translation of Symmachus was completed in the early second century CE. Jeremias wants to claim that the OG Isaiah translator’s connection of akrogōniaios with foundations and not capstones is idiosyncratic. However, the fact remains that this is the only usage of this noun attested before the writer of Peter uses this citation. The use by Symmachus occurs a century later  than 1 Peter and may equally be idiosyncratic.