If alienation (and not sin) is the main self-perceived malaise of modern man - and alienation is life as purposeless, meaningless and the human self as isolated from relationships with the world - then the cure for alienation is mysticism.
If modern Christianity lacks a significant mysticism, then it will fail to attract the alienated souls - who will either dull their pain with distractions and intoxicants, or look to non-Christian spirituality and mysticism.
Yet mysticism was, and is, an aspect of Christianity, part of the fullness of Christianity.
Christian mysticism is directed at attaining communion with God. An example is the Orthodox Hesychast tradition which may involve ascetic disciplines and prolonged prayer (The Jesus Prayer, and similar short repeated prayers).
However, this solitary striving is pursued under monastic discipline, accompanied by frequent daily participation in numerous formal religious rituals and liturgies.
From a Christian perspective, detached mysticism, solo mysticism - indeed any seeking of advanced and unusual religious experiences outwith Christianity - is hazardous, indeed may be spiritually fatal (that is, fatal to salvation) - because its motivations are flawed: sensation-seeking, power-seeking and pride.
For Christians, pride is the worst of sins, because it sets the self above God, and mystical striving has a strong tendency to induce spiritual pride - which may be very resistant to correction.
There is also a non-Christian 'aesthetic' mysticism which may be well-motivated, implicitly motivated towards communion with God - albeit incompletely so, absent the necessary mediation of Christ.
This high motivation will - however - tend to become corrupted by sensation-seeking, power-seeking and pride; since these are powerful and the fallen human has - if unaided by Grace - no ability to resist (or even identify) that which is intrinsic to his nature.
So - the main mystical tradition in Christianity is in Eastern Orthodoxy - and that is the path of asceticism under monastic discipline - the Via Negativa (Negative Way), the path of rejecting the world and worldly distractions, aiming at a direct approach to God, by Love of Christ.
But Charles Williams emphasized the other mystical path, the Via Positiva or Positive Way, the indirect aim - the aim at becoming more Holy via love of God's creatures (i.e. God's created things and beings).
This is the Christianity of Man engaged with the world - engaged with art, music, philosophy, mathematics, crafts, farming, care of a family...
And especially it is the path of Mysticism of Love - what C.W. called Romantic Theology.
Thus the path of the Positive Way, the Love of created things, is often through the mysticism of marriage and family.
A recognition that marriage is sacred, a sacrament.
Interestingly, the greatest, most focused modern Christian exponents of the Via Positiva are Mormons - whose distinctively concrete theology places the married couple and their children at the centre of God's plan of salvation - such that the highest salvation is available only to the married, and mystically sealed marriages and families are continued into the afterlife. Perhaps as a part of the same emphasis, Mormons reject the Via Negativa in its purest form - there are no Mormon monasteries (at least, not yet).
Modern Christianity needs, as a matter of extreme urgency and importance, to restore its mysticism. It needs to restore the use of sublime language, music and architecture; to encourage a revival of monasticism; and also it needs to restore the mysticism of Love, Marriage and Family.