Theosis is a term for the process of divinization, sanctification or spiritual progression which Men are meant to undergo during mortal life.
So the task of mortal life can be summarized as: attaining salvation (not damnation) and - on top of this - moving as far as possible towards the same level of being as God (alternatively, which means the same, of becoming more Christ-like).
I regard theosisconceptualizing degree of theosis : For instance person A has gone two feet up the path, person B, two hundred yards, Saint C a mile and a half...
This linear metaphor works well enough in those branches of Christianity when ascetic monasticism is seen as THE path to sanctification and each person can be measure by the progress along this path - and even Saints can be ranked: For example among Old English Saints, Cuthbert is judged to have ascended higher than the Venerable Bede (great Saints although both were).
But when theosis is not seen as a single path, when for example Marriage and Family life are seen as potentially a greater path to salvation than monasticism, there is the problem that each marriage and each family is unique in a way that each monk is not. We have moved from a model of theosis in which everyone attempts to conform to a single, perfect but not-fully attainable ideal to one in which each person is seen as intended to be unique.
That is, at any rate, how I understand these things: God wants us each to become more fully ourselves so that ultimately Heaven will be populated by a vast multiplicity of distinct persons; all spiritually advanced and still advancing - all relating to one another as peers or siblings: in essence, on a level of friendship.
Here in mortal life we have rules and constraints, which ultimately derive from the nature of reality, and which are for our Good: these include summaries such as the Ten Commandments, and other laws and regulations. Theosis must proceed within these boundaries; and when, as inevitably happens, we fail to live up to this ideal, we need to repent by acknowledging our failure and endorsing the revealed reality of the nature of things.
But in the context of these rules, these constraints, our destiny is theosis - to advance spiritually; or rather, not so much to advance as to build our own pattern. So theosis can be seen as - for each of us - a destined pattern - or type of pattern, towards which we grow and which we increasingly elaborate.
But 'pattern' is too abstract, geometric, and simplified a word: we are organic beings. So perhaps a better metaphor is a tree - we are each a type of tree (an oak, beech, birch, blackthorn) and our destiny is to become a mature example of that tree - and, of course, all individual trees are different and in a sense meant to be different (due to their initial innate differences, differences in experiences, and in a sense different choices during maturation and growth).
All metaphors break down if pushed, and this is no exception - but at a first level of analysis we might thing of our life on each as a period of growth, maturation, elaboration within proper bounds and towards something which is both characteristic and unique - like a particular oak tree.
And that God does not want all His trees to be oaks, nor does he want all his oaks to be identical - but for each to be the best of its kind and most fully developed of its nature.
In the end, the purpose of this post is simply to illustrate that our metaphors do constrain our thoughts, and that we need some more elaborate and personal metaphor to self-explain the (mostly unfamiliar) concept of theosis than the usual one of everybody progressing up along a path in single file.
Mortal life is, and is meant to be, complex and multi-faceted - and each person's life is both characteristic and distinctive - and our thinking ought to reflect that.