The spiritual life is the progress of the finite creature towards union with the Infinite. In all its stages the process of being conformed to God is going on in the soul. Nothing is indifferent. Every moment of time may be made to bear the burden of something which is eternal. Each separate action, no matter how trivial, is capable of holding a supernatural intensity. The grace, which enables us to do supernatural things, is coming to us constantly in ways that are imperceptible except to the greatest vigilance, and operating in us with such fineness and delicacy as require heavenly discernment, in order that we may perceive them, and cooperate with them. On the other hand, the unworthiness of our nature is almost unbounded, and its manifold unfitness for such a divine union is disabling us at every turn. .... Moreover nature to the last draws one way, and grace from the first draws another. Thus the three leading characteristics of the spiritual life must always be effort, detail and slowness, all three things monotonous, and all three almost insufferable monotony.
If you think that last sentence does not seem to follow directly from what precedes it, the following may help:
EFFORT: this is the perseverance to keep all our actions and thoughts fixed on God. It is an act of the will, and it can have a severely weakening effect on the body. It is an act of love. It is more like the slow patient effort of a needlewoman rather than the energetic effort of a sprinter. Also, if the effort is some sort of constipated straining then it is wrong. Such effort is desirous of a particular outcome, comes from self and is directed towards the pleasures of self. No matter how "religious" its motivation it is little more than the desire for release from painful verstopfung for relief's sake.
DETAIL: recall Faber says "nothing is indifferent". Everything has significance. This includes your dress, your breathing, your tidiness, your deportment, how you read words and how you read people, even how your fork approaches your food. (A fasting person can still be a glutton). This is not introspection, detailed self-awarness, when the focus isn't self but mastery of self and ultimately forgetfulness of self is an important step to see if your motives for dressing up/down, fast/careful talking, food likes/dislikes are actually all simply pride. Understanding detail requires mastery of simplicity. This is a lifetime's work.
SLOWNESS: effort and detail require nothing is hasty. Even if you are called to pull someone from a fire, there must be a slowness and stillness in you that are the opposite of panic and feeling like a hero. Let God work through you, that is the only heroism that counts.
This is the monotony that we must embrace, the monotony of the desert into which we plunge ourselves during Lent, to be alone with the Infinite Solitude.