The ‘I am.’ (Ἐγώ εἰμι)
In Exodus 3: 13-14, God introduces Himself to Moses by His Name “I AM”.
καὶ εἶπεν ὁ θεὸς πρὸς Μωυσῆν Ἐγώ εἰμι ὁ ὤν· καὶ εἶπεν Οὕτως ἐρεῖς τοῖς υἱοῖς Ισραηλ Ὁ ὢν ἀπέσταλκέν με πρὸς ὑμᾶς. – LXX
The Beloved Apostle writes the scene in the Garden this way, “Judas then, having received a band of men and officers from the chief priests and Pharisees, cometh thither with lanterns and torches and weapons. Jesus therefore, knowing all things that should come upon him, went forth, and said unto them, Whom seek ye? They answered him, Jesus of Nazareth. Jesus saith unto them, I am (εγω ειμι). And Judas also, which betrayed him, stood with them. As soon then as he had said unto them, I am, they went backward, and fell to the ground. (18:3-7)”
Before that that tense moment, John writes of another occasion, when Jewish leaders told Christ, “You are not even fifty years old, and you have seen Abraham?” Jesus answered them, saying, “Verily, verily, I say unto you, Before Abraham was, I am.” In the Modalist view, this passage as well as the above, makes sense. This does not point to the pre-existence of the Son, since that has already been proven an erroneous assumption, but to the very truth that Christ was God manifested in the flesh.
In John 8:24, Christ says, “I said therefore unto you, that ye shall die in your sins: for if ye believe not that I am (οτι εγω ειμι), ye shall die in your sins.” ‘He’ is inserted in many translations, but no word exists in Greek for the pronoun after the copula ειμι. It simply means ‘that I am’. The Jews (Deuteronomy 32:39) used the language when speaking about the LORD (In Septuagint Isaiah 43:10 the very words occur πιστεύσητε καὶ συνῆτε ὅτι ἐγώ εἰμι). The phrase εγω ειμι occurs three times here (John 8:24, John 8:28, John 8:58) and also in John 13:19 and 18:5.
“‘He’ is inserted in the versions and is not in the text. By retaining it, we read, I am the Messiah. But the words are rather the solemn expression of His absolute divine being, as in John 8:58 : “If ye believe not that I am.” See Deuteronomy 32:39; Isaiah 43:10; and compare John 8:28, John 8:58 of this chapter, and John 13:19.”
‘Already in the LXX ἐγώ εἰμι is used for God (Ex. 3:14). Philo has it too, and it is a divine predicate in Josephus. In the NT Revelation uses it in the formulas in 11:17; 1:4, 8; 4:8 — formulas of worship, salutation, and self-predication. The nondeclinability of ἐγώ εἰμι and the quasi-participial use of εἰμι preserve the sanctity of the divine self-predication. The formulas express God’s deity and supratemporality. Similar formulas occur in Judaism. The Greeks also use two- and three-tense formulas to express eternity (cf. Homer, Plato, and an Eleusinian inscription). These possibly came into Revelation by way of the Jewish tradition, though a common source may lie behind the Greek and Jewish traditions.” Kittel further says that ἐγώ εἰμι is a self-designation of Christ which ‘stands in contrast to the genésthai applied to Abraham’.
The point of ἐγώ εἰμι is not Christ is identifying himself as the Messiah or a second part of a Trinity, but as the Absolute Deity Himself.
With this said, how can we avoid the Patripassian misunderstanding of Tertullian? We have to still remember that God, preexistent and eternal, manifested Himself in the flesh, creating the Son in His humanity. The Son who revealed to humanity God, who bore the name of God, and who could rightly claim that He was God, was not the Father. It was the human nature of the Son that died and rose again, suffering the agonies of the Cross, and baring upon Himself the sins of the world, of you and me.
 ἴδετε ἴδετε ὅτι ἐγώ εἰμι, καὶ οὐκ ἔστιν θεὸς πλὴν ἐμοῦ· ἐγὼ ἀποκτενῶ καὶ ζῆν ποιήσω, πατάξω κἀγὼ ἰάσομαι, καὶ οὐκ ἔστιν ὃς ἐξελεῖται ἐκ τῶν χειρῶν μου.