Catholic and Orthodox theology teach a doctrine called “theosis” or “deificatio”, which means “to be made God.” There are several scriptures which reveal this complex theology. It was also expounded upon by many of the Church Fathers, many of whose quotes are summed up in the Catechism of the Roman Catholic Church 460:

The Word became flesh to make us “partakers of the divine nature”: “For this is why the Word became man, and the Son of God became the Son of man: so that man, by entering into communion with the Word and thus receiving divine sonship, might become a son of God.” “For the Son of God became man so that we might become God.” “The only-begotten Son of God, wanting to make us sharers in his divinity, assumed our nature, so that he, made man, might make men gods.” 

In an attempt to maintain this theology while preserving God’s supreme glory as the only God, as if God has rivals, many have said such things as this:

1) We become a god, or we become gods. This pluralizes the divine, and makes humans lesser “gods”. Psalm 82:6, quoted by Jesus, calls all men “gods.” This is nothing special, as God has already pronounced it for all men (cf. Gen. 3:22). Thus, if we are to be transformed in Christ, we must be exalted above the lesser gods that we already are.

2) We become like God. This is theologically impossible. God is supreme, above all things, as their principle cause. Thus, to be “like” God is to be a being of likened power and sovereignty, like the dualist “good God vs. bad God” theology of many Gnostics. Exodus 15:11 says that nothing is “like God”. Michael the Archangel’s name means “Who is like God?”, a reference to this verse. Thus, no one can become like God.

3) We become parts of God. This comes from the idea that Christ is God, that the body of Christ is the Church, and that the members of the Church are the parts of the body. The conclusion is, then, “We are parts of God.” However, this is false. God is eternally simple, partless, non-composite. To be a “part” of God is to suggest that without you, God is incomplete. Is anything more prideful? The Church is contingent upon faith, but as faith is fundamentally related to ignorance, which in God is not found, God does not have faith. Therefore, the Church is not God, it is only his earthly body - as his Spirit lives in all those with faith. Thus, we remain parts of the Church, of the Body, but not of God. 

Now, the first is true of living saints, as those closest to God have God living through them. Thus, these Saints are deified in a limited sense. They are “gods” because they are divine people while still individual in the world. Of this Paul says, “…it is not I that live, but Christ who lives in me.” The Catechism of the Catholic Church 1988 says of this: 

…For this reason, those in whom the Spirit dwells are divinized.’”

Thus, the Orthodox and Catholic theology that a person is deified while remaining distinct from God is sound, in relation to living saints. But what about after death? This is where the Church breaks from reason. 

The actual theology is, “We become, by grace, what God is by nature.” This is a fairly straightforward statement. However, it is often accompanied with:

“…but this does not mean we become God or even like God. We are still distinct from God.” 

Let’s question this for a moment. What is God by nature? God’s nature is God himself. His existence is not in anyway separable from what he is. So God is God by nature. This is why Saint Peter says that we become “partakers in the Divine Nature.” The Divine Nature is what makes God, God. If we partake in what God is by nature, and yet, are not God, then God is not God by nature; this would imply that there is a being greater than God that made God what he is. However, this is absurd. God is, by nature, God. Thus, if we become what God is, by nature, we become God. As God, we are thus God by nature, as God can never not be God.

Therefore, we become by grace what God is by nature, and by that nature, we are what saved us through grace. In other words, we neither become gods, nor like God, nor parts of God; we simply become God, and there is only One.  

(Source: innerchrist)