Diodorus of Tarsus/Diodore of Tarsus did not teach salvation was a life long process (theosis/deification)

There happens to be an anachronism that Diodorus of Tarsus, or some say Diodore of Tarsus taught theosis, this is not true.

We can understand this by reading his text.

“Necessarily he set forth ‘those who call upon him.’ For God does not give grace without discernment, extending it even to those who are unwilling to offer so much to the Benefactor as at least to ask and pray with him. And lest anyone say that many fail to call upon the Lord Jesus out of ignorance rather than unbelief and ingratitude, he shows through what follows that God took away even the excuse of their ignorance, sending evangelists and heralds who urge and invite them to ask for the gift. Therefore he added what follows.” - Diodorus of Tarsus/Diodore of Tarsus, Romans 10:11-13.

εὐαγγελιστὰς καὶ κήρυκας (evangelists and heralds/preachers)

ἄγνοιαν (ignorance) and ἀπιστίαν (unbelief)

προτρέποντας καὶ καλοῦντας εἰς τὴν τῆς δωρεᾶς αἴτησιν (urging and calling them to the asking/request of the gift)

αἰτῆσαι καὶ δεηθῆναι (to ask and to pray/beseech)

The gift of God is to be understood as being in reference to salvation. We know this to mean that, and we know that he did not teach theosis, because Diodorus of Tarsus, or some say Diodore of Tarsus, wrote that a gift can be immediately accepted.

“This seems to contradict the preceding statement that “death spread to all men.” For having spoken above about all, he now speaks about many. But one must know that death indeed spread to all, since all also sinned, but it spread to all examining and testing them, taking hold not of those who simply sinned, but of those who persisted in their own sins, which he also makes clear through what follows when he says that “the many were made sinners,” through which he indicates the immutability of their wickedness. So death did spread to all examining them, seeing them sinning, but it did not put all to death. Some, then, thought to indicate a difference in death through these words, and that through the word “all” bodily death is indicated, but through “many” spiritual death. But the sequence of the argument now shows none of these things. For there is no distinction in it, but he speaks as if concerning a single universal matter. He is eager, however, to show that even if the transgression of Adam was devised by the evil one, who was securing for himself the beginning of his kingdom over men, yet the Lord by his coming bestowed a greater gracious gift." - - Diodorus of Tarsus/Diodore of Tarsus, Romans 5:15

ἐχαρίσατο/bestowed (echarisato) is in the Aorist tense/past tense

“Instead of corresponding to the one sin of Adam, the gift was great and abundant and surpassed the sins of all by its love for mankind, which he teaches by adding: “For the judgment from one resulted in condemnation, but the gracious gift from many trespasses resulted in justification.” For he means to say that Adam’s sin was one, but nevertheless, being one, from one sin it condemned the many because they imitated Adam. But the gracious gift of the Lord was not measured against one sin, but against the sins of all, which were many. So delivering them from many trespasses, he brought them into justification. For in this is the abundance of grace, that it not only delivered from trespasses, but also guided them into righteousness.” - Diodorus of Tarsus/Diodore of Tarsus, Romans 5:16-17

ἀπαλλάξαν (apallaxan)/delivered in "delivering them" is in the Aorist tense, past tense.

ἀπήλλαξεν (apēllaxen)/delivered in "delivered from trespasses" is in the Aorist tense, past tense.

ἐχειραγώγησεν (echeiragōgēsen)/"guided" in "guided them into righteousness is in the Aorist tense, past tense.

To say that, Diodorus of Tarsus/Diodore of Tarsus taught theosis/salvation is a life long process (deification) is to misunderstand the greek verbs.