Same Confession, different context
This is one of the cases where John differs most from the Synoptics which, in spite of their differences (Matt 16:13-20; Mark 8:27-30; Luke 9:18-22), have these elements in common (which we don't find in John):
- The location (Caesarea Philippi), not mentioned by Luke, though;
- Jesus' question on peoples' opinion, “Who do people say that the Son
of Man is [I am]?”
- The answer of the disciples (John the Baptist, Elijah, Jeremiah one
of the prophets - and variants thereof)
- Jesus' question on the disciples' opinion (“But who do you say that I
am?”)
- Peter's answer on behalf of the twelve (“You are the Christ, the Son of the living God.” - with variants in Mark and Luke)
- Jesus' approval of Peter (only in Matthew)
- The much disputed sentence of Jesus, "And I tell you that you are Peter, and on this rock I will build my church, etc." - only in Matthew
- Jesus' warning to keep secrecy
- Jesus prediction of his suffering, rejection, killing and resurrection (only Luke)
The core of Peter's confession in John is this verse:
We have come to believe and to know that you are the Holy One of God!”
(John 6:69)
It is worth reproducing here the footnotes appended by NET Bible at the end of the verse:
3tc The witnesses display a bewildering array of
variants here. Instead of “the Holy One of God” (ὁ ἅγιος τοῦ θεοῦ, ho
hagios tou theou, Tertullian has ὁ Χριστός (ho Christos, “the
Christ”); C3 Θ* Ë1 33 565 lat read ὁ Χριστὸς ὁ υἱὸς τοῦ θεοῦ (ho
Christos ho uios tou theou, “the Christ, the Son of God”); two
versional witnesses (b syc) have ὁ υἱὸς τοῦ θεοῦ (“the Son of God”);
the Byzantine text as well as many others (Ψ 0250 Ë13 33 Ï) read ὁ
Χριστὸς ὁ υἱὸς τοῦ θεοῦ τοῦ ζῶντος (ho Christos ho uios tou theou ho
zontos, “the Christ, the Son of the living God”); and Ì66 as well as a
few versions have ὁ Χριστὸς ὁ ἅγιος τοῦ θεοῦ (“the Christ, the Holy
One of God”). The reading ὁ ἅγιος τοῦ θεοῦ is, however, well supported
by Ì75 א B C* D L W as well as versional witnesses. It appears that
Peter’s confession in the Synoptic Gospels (especially Matt
16:16) supplied the motivation for the variations. Although the
witnesses in Matt 16:16; Mark 8:29; and Luke 9:20 vary
considerably, the readings are all intra-synoptic, that is, they do
not pull in “the Holy One of God” but reflect various permutations of
“Christ”/“Christ of God”/“Christ, the Son of God”/“Christ, the Son of
the living God.” The wording “the Holy One of God” (without “Christ”)
in important witnesses here is thus unique among Peter’s confessions,
and best explains the rise of the other readings.
sn You have the words of eternal life…you are the Holy One of God! In contrast to the response of some of his disciples, here is the
response of the twelve, whom Jesus then questioned concerning their
loyalty to him. This was the big test, and the twelve, with Peter as
spokesman, passed with flying colors. The confession here differs
considerably from the synoptic accounts (Matt 16:16, Mark 8:29, and
Luke 9:20) and concerns directly the disciples’ personal loyalty to
Jesus, in contrast to those other disciples who had deserted him
(John 6:66).
Conclusion
In spite of the absence of many of the elements that are present in the Synoptics, the one we find in John 6:69 is essentially the same confession of Peter's that we find in Matthew.
The expression "the Holy One of God", far from being unique to the Gospel of John, is even used by Peter, speaking of Jesus, in Acts:
But you rejected the Holy and Righteous One and asked that a man who
was a murderer be released to you. (Acts 3:14)