Why is the Church, after having evangelised the West and ruled it for a thousand years, allowing it to slide back into paganism?
The answer to this question is that she herself is unwittingly paganising it.
I mean by this that, without intending to do so, she is compelling it to choose between secularised life and arrested growth.

Were a growing tree encircled with an iron band, the day would surely come when the tree, by the force of its own natural expansion, would either shatter the band or allow it to cut deep into its own stem.
The growing consciousness of Humanity has long been encircled by a rigid and inadequate conception of God.

The gradual secularisation of the West means that the soul of man is straining that particular conception of God to breaking-point: and it is infinitely better that it should be broken to pieces than that its iron should be allowed to sink deep into the soul.
The secularisation of contemporary life means this, and more than this.

It means the gradual handing back of Man's life to the control of Nature,--of Nature which is as yet unequal to the task that is being set it, owing to its having been through all these centuries identified with its lower self, taught to distrust itself, and otherwise misinterpreted and mismanaged, but which, in obedience to the primary instinct of self-preservation, will gradually rise to the level of the responsibility that is being laid upon it.

With the further secularisation of Man's life, the need for religion to make effective the control of Nature, by pointing out to it its own ideal and so co-ordinating and organising all its forces, will gradually make itself felt, and the regeneration of religion will at last have begun.
* * * * * For many centuries the current of religious belief in the West was almost entirely confined to the one channel of Catholic Christianity.
There the mighty river pursued his course, "brimming and bright and large," till the time came when, with the gradual loss of his pristine energy-- "Sands began To hem his wintry march, and dam his streams And split his currents"; Side channels were formed, and grew in number; and though Catholicism is still the central channel for the moving waters, the river has now fallen on evil days, and "strains along," "shorn and parcelled," like the river of the Asian desert-- "forgetting the bright speed he bore In his high mountain cradle." Of the many side streams into which Western Christianity has split, the majority may be spoken of collectively as Protestant.
Protestantism claims to have liberated a large part of Christendom from the yoke of Rome; and it is therefore right that we should ask ourselves in what sense and to what extent it has brought freedom to the human spirit.