A topic of continuing interest to me;)
In recent weeks I have been finding a little solace with a few of the Churches so-called 'mystics.' Thomas A Kempis, St John of the Cross, Augustine, Madame Guyon...and I would include in that list Oswald Chambers and Amy Carmichael. I would say provisionally they are echoing some of the intimacy in the Spirit exhibited by the prophets and apsostles who wrote of spiritual truths in the scriptures, like John and Paul. However, their echoes are like all echoes of the real voice, changed and imperfect.
Regarding Tozer; Perhaps we can say he was addressing a false dichotomy...one that nevertheless is very much real in our day.
I say it is false, because if one does indeed hold to God's objective revelation, then they must personally encounter, experience, endure, enjoy, yea even enjoin with the living Spirit of God or they deny the claim of that objective revelation.
Take for instance Philippians 2;
If there be therefore any consolation in Christ, if any comfort of love, if any fellowship of the Spirit, if any bowels and mercies...Let this mind be in you, which was also in Christ Jesus:...For it is God which worketh in you both to will and to do of his good pleasure.
These verses explicitly tell of a communion of the Spirit, and it would be incongruent to believe these verses on an objective level without also experiencing them inwardly on a personal intimate level. To claim belief in one without the other is a farce.
Still the farce of fundamentalist doctrinal memorization is alive and well in our churches today. Given this context, insisting that a believer must have a "mystical union" with Christ is perhaps a needed distinction for the poor church veteran who knows bible verses, but not Christ himself.
However, if being satisfied with objective adherence is one farce alive and well in our religious age, then being satisfied with subjective experience is another farce that is also alive and well in our New Age. I've seen pitfall after pitfall, where Christian make claims ranging from the silly to the superstitious to the sanctimonious all because they were encouraged to cut the scriptural tether and float away. Men abandoning their familial duties because of high-minded visions, women on the floor convulsing indecently in public as they 'birth' new ministries...
What's more, I find that the personality attracted to the cultivation of mysticism tends to be the creative person, the thoughtful brooding melancholic, the introspective artist. I am that very kind of person myself...which is why I hold an extra wary eye on mysticism. My self-admission tells me two things; one, I should refrain from looking down my nose at less emotive or expressive saints whose testimony seems less mystical, less intimate, less romantically expressive, but more natural and simple. Often these simple men, who seem better suited in the natural world, are more like Christ is in the natural world, then I am when I am living in the mystical world.
And secondly, my self admission puts me on warning, because I know what kind of swirling imaginations I am capable of...and believe I can never allow myself to stray from the light of scripture off on my own quest for spiritual self-realization. At the risk of sounding immodest, my artistic imagination is far too creative, to be allowed to roam free range...that is if I want to see truth established within my mind and built up in my life. Despite my spiritual flights of fancy, I must learn to walk a more humble path and the scriptures are just the thing to keep it real. I do not trust someone who regards the printed word of God as mere elementary teachings...for I know within my indefatigable mind are a thousand tower of Babels kept unrealized and unconstructed by the discipline of that objective Word.
So I feel we can use the word 'mysticism' as a way to describe our living union with Christ only as long as our experiences support the testimony of scriptures, but never supplant them.
I'm paraphrasing I think Dwight Moody when he was asked which is more important: Reading the scriptures (objective life) or prayer (subjective life). He answered with his own question, "Which is more important to a bird, his right wing or his left wing?" Objective and subjective, inward and outward, natural and supernatural...they are both wings on the same bird. To imply that one is more important then the other leads to confusion!
(edit: these are just my loose thoughts on the topic, and certainly not a position I would hold other people to)
MC