Ἰωάννην 15·26 Ὅταν ἔλθῃ ὁ παράκλητος ὃν ἐγὼ πέμψω ὑμῖν παρὰ τοῦ πατρός, τὸ πνεῦμα τῆς ἀληθείας ὃ παρὰ τοῦ πατρὸς ἐκπορεύεται, ἐκεῖνος μαρτυρήσει περὶ ἐμοῦ· 27 καὶ ὑμεῖς δὲ μαρτυρεῖτε, ὅτι ἀπ᾿ ἀρχῆς μετ᾿ ἐμοῦ ἐστε.
Whenever the intercessor comes, who I will send to you from the Father: the spirit of truth which goes out from the Father, that one (the intercessor) will testify about me. And you will also testify about me because you are with me from the beginning.
ἐκεῖνος “that one”
Most translations render ἐκεῖνος as “he”. In this passage, ἐκεῖνος can’t refer to τὸ πνεῦμα “the spirit” because τὸ πνεῦμα is a neuter word while ἐκεῖνος is a masculine word. The only noun that ἐκεῖνος can be referring to is ὁ παράκλητος, “the intercessor”. I know we are splitting hairs here, but I wanted to bring out how the Greek is working in this passage.
ὅτι ἀπ᾿ ἀρχῆς μετ᾿ ἐμοῦ ἐστε. “because you are with me from the beginning”
Most translations render this, “because you were with me from the beginning.” The greek “to be” verb here is in a 2nd person plural present tense. In Koine Greek, the present tense carried an aspect of a continuing action. So, the disciples were continually with Jesus from the beginning of his ministry. John could have used an Imperfect tense that is past time, continual aspect, but he chose to use a present tense verb. What does that tell you about how Jesus felt about the disciples remaining with him?