It is a huge subject, and requires a lot of effort to understand.
Nothing is accidental in the use of Greek words for the Bible by the apostles and evangelists of Christianity.
The text says "angle head", not "cornerstone". The concept has nothing to do just with a cornerstone (i.e. only the edge and the stone); The phrase is: "The head (edge) of the angle", therefore, the angle is included in the text, whereas if we say just "cornerstone" (i.e. the edge stone), then, the angle (the two sides) is not included, and that is which includes all the meaning. This is a highly allegorical concept, and the stone is understood as a point on a building that acts as in an angle, the head (edge) of the angle.
The translation is this
The stone which the builders disapproved, this was appointed as the head of the angle: this, it was done by the Lord, and is marvelous in our eyes!
I think we have to travel way back in time to understand these words and the meaning of their connection in the sentence. And I will try to do so.
I may get a bit tedious in referring to various things, but it is important to understand words that have a deeper meaning.
It is important to understand the root of the word "γωνία" (ghonía), and the ancient symbolic Semitic letters, because the Greeks, it is said, got the alphabet from the Phoenicians. This means that most languages that exist today, if not all, are branches of a common language.
The word "γωνία" (noun [English angle, Latin anguli]), comes from the also noun "γόνυ" (the angle formed by the foot; the knee, the angular part of the foot). It has "ω" and not "o" because it forms a large angle (Ω mega), and the word is in the feminine gender, because, as we define the words of the feminine gender in Greek with the definite article "H", in ancient times something big and special was meant; taken from the Semitic letter (Hebrew ח [het], the English letter “H” as a consonant of exhalation, which represented in pictographs a great dividing wall indicating that which is beyond it, as something impossible to reach, and sublime; i.e. beyond the limits of man).
The word "γόνυ" (Lat. genu, Eng. knee, N. Gr. γόνατο), essentially, also functions, as a connection, connecting the base of a man's or animal's leg, with the rest of his upper body; but also as a base, when we fall to our knees (or bend our knees) to beg someone, to not harm us, which indicates an act of safety ("αγκωνάρι" [agonáre] = massive cornerstone which used for buildings, from ἀγκών [agón] = elbow) or to pray to God. A Greek word is "γονυπετέω" (ghonepetéo) < "πίπτω γόνυ" (pépto ghóne [to fall on my knees]), "κλίνω γόνυ" (kléno ghóni [to bend my knees]).
The first meaning, which functions as a connection, must have deep roots in antiquity, and this is, I believe, in essence, the meaning identified by the biblical phrase "κεφαλὴν γωνίας" (kefalén ghonéas). I don't think it has to do with the “αγκωνάρι” (agonári) of a building, which supports the building from a corner, as we would interpret it as: the basic or head corner support of the building, and be that Christ. e.g. Christ set Peter up as a rock, though not in the sense of an αγκωνάρι (agonári), but as the base, which functions as the initial structure. Therefore, it cannot be understood that Peter is the basis and Christ is one of the three or four agonári of the structure (of the Church). Here, of course, the Lord's rich gift to Peter is also implied (a rock, as a base), and its rich meaning, which gives Peter immense honor, will be fully understood below.
The word "γόνυ," has a root of two consonants and a semi-consonant "γνυ"; the "o" marks, perhaps, the small shape, referring to the foot (probably "Y" [with the sound "w"] was originally "F" [same sound propably], which, both of which, have the sense of a pillar, which fastens a building. The "Y", has the image of an ancient cup [ancient glass] which is in the shape of a "Y", and it holds water, or wine). The letter "Γ" (with sound "gh", the 3rd letter of the alphabet) is a foot, which also is an ancient iconography of the letter, while the letter "N" (with sound "n"), according to the information we have from ancient pictographs, symbolizes an infant. An infant, as we know, walks on its knees. The "γνυ", i.e., here denotes, perhaps, the part of the foot by which the infant walks and supports its body, or the walking by which the infant supports itself (knees). The connection (united) is shown to be one with the ground. So, in general, "γνυ" (knee) has the meaning of the property which joins a base (ground) to the rest of the body (infant).
In this case, we have three meanings.
Introduction to the name of Peter
Πέτρος (Pétros > Peter), taken from the Hebrew word "כֵּיפָא" (kephá) which has the meaning of "holding the passage (which comes under the base)". On the other hand, one sense of the word "πέτρα" means a massive stone; But the Hebrew or Aramaic name, since it originated there, should be considered in the ancient letters to determine the meaning. It is certain that the letter Π (with the sound "p"), both in Hebrew and Greek, marks a gate, a passage. The vowel (the next letter) does not reveal a relevant meaning to me, so it is probably an auxiliary pronunciation vowel. The next letter is T; this letter does not mean a closure or hold, but it does mean its derivative, which comes from the same ancient Phoenician, X; the X in front of the Π closes the entrance. Generally X and T are two rods, two bars. So Matthew chosed to use the T, because he is Aramean and he formed in his mind the equivalent letter of the ת (taw); I don't know if he had in his mind the X with the same meaning. However, the next letter Ρ (sound "rh"), I am not sure what it means here; this letter generally marks a flow, as well as a mindset or spirit of a person. If it has to do with the meaning of the Greek word "ῥύω" (rhéo) beginning with "Ρ", and meaning "to turn away, to free”, i.e. from bad circumstances, where the original meaning is perhaps, from what I can see, "to support the spirit, to judge righteously", then perhaps, the word Πέτρος (ΠΤΡ [the “o” and “ς” indicates masculine gender]), may mean "the support of Christ by the closing of the passage". Is of course a conjecture, but it is still a logical conclusion.
(cf. Epistle to the Ephesians 2,20-22)
- Here we have an elbow (L bow with right-angle); where the base is Peter, taken from the Hebrew word "כֵּיפָא" (kephá) which has the meaning of "holding the passage (which comes under the base)", i.e., what Jesus said in Matthew: “κἀγὼ δέ σοι λέγω ὅτι σὺ εἶ Πέτρος, καὶ ἐπὶ ταύτῃ τῇ πέτρᾳ οἰκοδομήσω μου τὴν ἐκκλησίαν καὶ πύλαι ᾅδου οὐ κατισχύσουσιν αὐτῆς” (Matthew 16,18). Which means: "And I say to you that you are Pétros, and upon this Pétra I will build my Church, and the gates of hell shall not prevail against her." The head (edge) of the angle is Christ who holds his body, and together with the twelve apostles and Paul, they lay the foundation and upon them the Church is built, who are all Christians in general, including Jesus Christ and the apostles, including Peter, i.e. the body of Christ, the elbow (L).
(cf. Epistle to the Ephesians 2,11-19)
- a) The other explanation, is the elbow (L bow, which means right-angle) in the sense of a connection again, where it joins the two parts of the arm; where arm, according the ancient iconography, means the power of man, etc; by extension, the power of the Son of man (of Jesus Christ), where his power is his people, and whom he constitutes. The base of the L is the old Israel. The difference is that the old Israel fought to occupy territory on earth, lived for the interests of his flesh, and looked with his face to the earth, so the base of L is the old Israel; while the new Israel fights to occupy territory spiritually, lives for the interests of others, and looks with their face to heaven, so the upright part of L is the new Israel (Christians). On the other hand, the Law was set as a basis, as a principle. The basis of the Moses. Also, Abraham, Isaac and Jacob (> Israel) are the three patriarchs, and from Judah David the king came, and from him Jesus Christ came, the head (edge) of the angle, now he came. And from there onwards there is an ascent, because the base is finished and the head of the angle has come and taken its place. Where together with the 12 apostles and Paul, they lay a foundation and the Christians are built on it and the Church takes shape, the shape of an angle. And now these two lines are united. b) Here the ideal letter of the alphabet which represents this angle with the two sides joined is the "A" (álpha). The pronunciation also of this is the separation, between those at inside (old Israel) and those at outside (Gentiles), driving out the separation with the blowing of the mouth. And what is awe-inspiring is the verb Paul uses "λύω" (léo [λύσας past tense participle nominative 3rd singular] Epistle to the Ephesians 2,14b), which perfectly expresses the meaning of his pronunciation. New Greek equivalent "διαλύω", English word "scatter". While the Hebrew equivalent letter is א (áleph). which is divided into two strands with a partition, separating the inside from the outside. Even the alphabet, while meaning other things in the beginning, concealed another meaning. Everything is destined by God!
(cf, Epistle to the Ephesians 2,14-16; All the Epistle to the Hebrews)
- a) Another elbow (L bow), even stronger view, is that the angle here means the change of course that forms an angle. That is, the turning from one line to another line of a different course. And the head of this angle, that is, the cause, is Jesus Christ, who was incarnated, crucified and resurrected to mediate between God and man and to abolish the sin that resulted from the transgression of the Law and to give a new way of forgiveness. And he made an angle of 180 degrees; and no longer does the people expect to be forgiven by the blood of the slaughter of animals, just as there is no holy of holies on earth, but in heaven; and so the people enter the holy of holies in heaven, directly to the Father through Jesus Christ, receiving forgiveness of sins by the blood of the now heavenly Lamb. It became a 180 degree angle. where Christ now acts as a priest, offering his own blood, not like the priests of the earth, where every time the high priest died, another high priest had to be appointed, whereas Jesus is the high priest, and the real priest, for eternity. (cf. see Epistle to the Hebrews). b) Again, here we have the so-called L bow, where the basis is the Law of Moses through the eyes of Jesus Christ, "Think not that I came to abolish the law or the prophets; I did not come to abolish but to fulfill", where he gave us his teaching, and then he ascended and sent the Spirit of help, exhortation, guidance in the truth, etc. And then he ascended and intercedes between man and the Father, sending the Holy Spirit. And this L bow unites those who come to God through Jesus Christ who sends the Holy Spirit and acts as the head of the angle, and unites man to God, the so-called engagement of the Spirit.