“I and the Father are one.”
Ἐγὼ καὶ ὁ Πατὴρ ἕν ἐσμεν (Egō kia ho Patēr hen esmen), lit., “I and the Father one thing we are”).
Both historically and currently, Christians have pointed to this passage to show that Jesus indeed claimed equality with God the Father. As with Jesus’ other undeniable claims to be truly God (Matt. 12:6; John 5:17-18; 8:58-59 et al; Rev. 1:7-8, 17; 2:8; 22:13; etc.), the response of the Jews in verse 33 hence, is an irrefutable confirmation of Jesus’ claim: “For a good work we do not stone You, but for blasphemy; and because You, being a man, make Yourself out to be God.”
This passage also provides a clear refutation to the Oneness view (as discussed below), which erroneously asserts that Jesus is the Father (the same person). Ironically, Oneness advocates actually use John 10:30 as a so-called proof text, aside from the fact that throughout chapter 10, Jesus and the Father are clearly differentiated as two persons (vv. 15, 17, 18, 25, 29, 30, 36, 37, 38).
However, the following points regarding John 10:30 clearly refute Oneness theology:
Not one person within conservative recognized Christian scholarship agrees with a Oneness interpretation. Neither historically nor contemporaneously has any Christian writer interpreted John 10:30 in a modalistic (Oneness) way. Rather, all standard scholarly sources (patristics, commentaries, grammars, lexicons et al), interpret the passage in the plain intended way, within the defining context: The person of the Son claiming equality with the distinct person of the Father.
Plain reading. Jesus simply says, “I and the Father ARE one.” Only by pretexting can one read something into this text beyond the simple plain reading.
The neuter adjective hen (“one”) is used—contextually indicating a unity of essence, not personal identity. If Jesus wanted to identify Himself as the same person as the Father (same person), He certainly could have used the masculine heis to indicate this (e.g., John 12:4; Rom. 3:10; 1 Tim. 2:5 et al.). In this passage, the Father and the Son are the two subjects of the sentence (egō, “I,” and Patēr, “Father”—both in the nominative [subject] case).
The neuter adjective hen (“one”) is the predicate nominative and it precedes the plural verb esmen (“are”). The predicate nominative “one” is describing the essential unity of the two subjects, Jesus and the Father.  In other words, Jesus is explaining that the Father and Son are one thing, not one person, in the context of unity, not identity of person. The same neuter adjective is used in John 17:21, expressing unity (not person) where Jesus prays that His disciples “may be one [hen]” even as Jesus and the Father are one. However, in verse 30, it was a unity in ontological coequality that Jesus expressed—thus, “The Jews picked up stones again to stone Him” (v. 31).
The plural verb esmen (“are”). Again, in sharp contrast to the false Oneness interpretation (viz., that Jesus is the Father), the Greek contains the plural verb esmen (“I and the Father are one”), and not a singular verb such as eimi (“am”) or estin (“is”) in which case, the passage would read: “I and the Father am/is one.”
Furthermore, Jesus’ claim to deity is not merely found in verse 30. But rather, the passages leading up to verse 30 undeniably prove His claim. In verses 27-29, Jesus claims that He is the Shepherd that gives His sheep eternal life and no one can snatch them from His nor His Father’s hand (same words of YHWH in the LXX of Deut. 32:39). The Jews were well acquainted with Deuteronomy 32:39: “And there is no one who can save anyone from My hand” and Psalm 95:7: “For He is our God, and we are the people of His pasture and the sheep of His hand.” The Jews knew that only YHWH could make these claims of having sheep in His hand and giving them eternal life (cf. also Isa. 43:11).
It was after Jesus made these familiar and exclusively divine claims that He stated, “I and the Father are one.” Again, not mere unity, rather, unity in ontological coequality. So, it is easy to understand the response of the Jews wanting to kill Him for blasphemy: “You, being a man, make Yourself out to be God [poieis seauton Theon]” (vv. 31, 33). If Jesus were only claiming to be “one” with the Father in the sense of mere unity, then Jesus’ claim would not have warranted blasphemy (Lev. 24:16).
 Renowned Greek grammarian A. T. Robertson comments on the application of the neuter hen in John 10:30: “One (hen). Neuter, not masculine (heis). Not one person (cf. heis in Gal. 3:28), but one essence or nature” (Archibald T. Robertson, Word Pictures in the New Testament [Nashville, TN: Broadman Press, 1932], 5:186).
 Deuteronomy 32:39 (LXX): “And there is no one who can deliver ek tōn cheirōn Mou [‘out of the hands of Me’].” John 10:28: “they will never perish; and no one will snatch them ek tēs cheiros Mou, “out of the hand of Me.” John 10:29: “no one is able to snatch them ek tēs cheiros tou Patros (“out of the hand of the Father”).
 As in John 5:18, in John 10:33, the second person reflexive pronoun seauton (“Yourself”) indicates that the Jews understood that Jesus’ claims in John 10, which culminated in verse 30 (“I and the Father are one”) were by and for Himself—namely, He Himself made Himself “out to God.”