God and the spiritual world are real. We can reckon upon them with as much assurance as we reckon upon the familiar world around us. Spiritual things are there (or rather we should say here) inviting our attention and challenging our trust.
Our trouble is that we have established bad thought habits. We habitually think of the visible world as real and doubt the reality of any other. We do not deny the existence of the spiritual world but we doubt that it is real in the accepted meaning of the word.
The world of sense intrudes upon our attention day and night for the whole of our lifetime. It is clamorous, insistent and self-demonstrating. It does not appeal to our faith; it is here, assaulting our five senses, demanding to be accepted as real and final. But sin has so clouded the lenses of our hearts that we cannot see that other reality, the City of God, shining around us. The world of sense triumphs. The visible becomes the enemy of the invisible; the temporal, of the eternal. That is the curse inherited by every member of Adam’s tragic race.
At the root of the Christian life lies belief in the invisible. The object of the Christian’s faith is unseen reality.
Tozer, A.W. (2013-11-08). Pursuit of God (Kindle Locations 641-649). Baker Publishing Group. Kindle Edition.