1 THESS 5:23 Now may the God of peace Himself sanctify you completely; and may your whole spirit, soul, and body be preserved blameless at the coming of our Lord Jesus Christ.
There is debate in theological circles over the makeup of ‘man’. Some say tripartite body, soul, spirit, some are dualistic, that is, body and soul are ‘one’.
It’s true that the soul and spirit are difficult to separate, in fact there is only one ‘thing’ that can separate them ..
HEB 4:12 For the word of God is living and powerful, and sharper than any two-edged sword, piercing even to the division of soul and spirit,
But, that ‘one’ thing is the ‘thing’ that matters. (The word). It’s in this understanding (of the makeup of man) that the understanding for you answer lies. If you don’t ‘see’ the distinction between soul and spirit, you will need to re-interpret much of Paul’s teachings..... including Colossians from which you are quoting...
It’s the numerous times Paul says that if you are a believer, then you are ‘in him’ or ‘in Christ’.
COL 2:10 and you are complete in Him
The ‘key’ to this is ...
2 COR 5:17 Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new.
What is ‘new’? What ‘part’ of you is a ‘new creation’? Body? Soul? or Spirit? Or is this merely ‘figurative’? This decision is yours to take, but whatever you decide, it will influence your interpretation of all of Paul’s teachings, every one of them. Bit, as I said, there is no agreement on this among theologians.
So when you asked, what does “Fullness of the Deity” mean in Colossians 2, the answers you get, and the answer you’ll accept depends on your viewpoint of ‘body, soul, spirit’. I say this (fullness of deity) is fulfilled ‘spiritually’, that is, via your recreated ‘spirit’. You (that is, your ‘spirit man’) has been reborn. New.
But you’ve already accepted another view so obviously won’t agree with mine. Nevertheless I post this for others to consider.