“And Thomas answered and said to him: My master and my God (Mori v’Elohi)” (Jn 20:28).
The phrase may have been taken from Psalm 35:23. Apparently Thomas is answering to Yeshua concerning his previous unbelief. Thomas is depicted in John as someone with many doubts. Yeshua had told Thomas in the past: If you know me, you would know my Father also, and from now [from seeing me and my teachings] you know him and you are seeing him (Jn 14:7). Now Thomas is recognizing that seeing the Tzaddiq is like seeing HaShem.
This title: Elohi, means divine and also means judge. It is not common to apply this title (Elohi) with the meaning of divine to a man. However it is not uncommon in mystical literature. We have a few references:
The term Elohim is applied to Moshe. He was Pharaoh’s Elohim, and Aaron was his prophet (Ex 7:1). The reason the title Elohim is applied in both senses to Moshe (both judicial and Divine) is for the prowess and miracles performed through his faith, and because of the prophetic level he reached (God spoke directly through him).
In the Zohar, the central hero, the maximum righteous (in the Sefirah of Yesod) is Rabbi Shimon bar Yohai. The Zohar says about him that he represents God’s face on Earth. Rabbi Pinkhas ben Yair kissed Shimon bar Yohai and exclaimed: “I have kissed the mouth of God, perfumed with fragrances of his garden” (Zohar 3:201b), the fragrances representing his teachings.
The following pesher from the Zohar shows how the righteous is indeed an agent, a visible face of God on earth:
“One day Rabbi Shimon was going from Cappadocia to Lyddia, accompanied by Rabbi Abba and Rabbi Yehuda. Rabbi Abba was weary, running after Rabbi Shimon, who was riding [on a donkey]. Rabbi Abba then said: ‘They will follow HaShem, roaring like a lion’ (Zohar 1:223a; quoting Hoshea 11:10 and applying it to Shimon bar Yohai).”
In the Hassidic world there’s another person dubbed with the title Elohi. Isaac Luria; known as the Ari. Ari is an acronym for “Elohi Rabbi Itshaq” (The Divine Rabbi Isaac). The reason he receives such a title is because he devoted his entire life to Torah study and meditation. He came to know the thoughts of people, for he turned away from the vanity of the materialistic world, and to him it was revealed the spiritual world every day of his life; he was able to understand the language of nature and to perform all kinds of miracles – as God was working through him (cf. haHakdamot Shaar, intro).
If Moshe, Shimon bar Yohai and Isaac Luria received a Divine name… it is of no surprise that the Messiah would be called in the same manner.