It is difficult to acquire or to practise this faith and steadfastness on the rough and narrow path of Yoga because of the impatience of both heart and mind and the eager but soon faltering will of our rajasic nature. The vital nature of man hungers always for the fruit of its labour and, if the fruit appears to be denied or long delayed, he loses faith in the ideal and in the guidance. For his mind judges always by the appearance of things, since that is the first ingrained habit of the intellectual reason in which he so inordinately trusts. Nothing is easier for us than to accuse God in our hearts when we suffer long or stumble in the darkness or to abjure the ideal that we have set before us. For we say, “I have trusted to the Highest and I am betrayed into suffering and sin and error.” Or else, “I have staked my whole life on an idea which the stern facts of experience contradict and discourage. It would have been better to be as other men are who accept their limitations and walk on the firm ground of normal experience.” In such moments—and they are sometimes frequent and long—all the higher experience is forgotten and the heart concentrates itself in its own bitterness. It is in these dark passages that it is possible to fall for good or to turn back from the divine labour.
If one has walked long and steadily in the path, the faith of the heart will remain under the fiercest adverse pressure; even if it is concealed or apparently overborne, it will take the first opportunity to re-emerge. For something higher than either heart or intellect upholds it in spite of the worst stumblings and through the most prolonged failure. But even to the experienced sadhaka such falterings or overcloudings bring a retardation of his progress and they are exceedingly dangerous to the novice. It is therefore necessary from the beginning to understand and accept the arduous difficulty of the path and to feel the need of a faith which to the intellect may seem blind, but yet is wiser than our reasoning intelligence. For this faith is a support from above; it is the brilliant shadow thrown by a secret light that exceeds the intellect and its data; it is the heart of a hidden knowledge that is not at the mercy of immediate appearances. Our faith, persevering, will be justified in its works and will be lifted and transfigured at last into the self-revelation of a divine knowledge. Always we must adhere to the injunction of the Gita, “Yoga must be continually applied with a heart free from despondent sinking.” Always we must repeat to the doubting intellect the promise of the Master, “I will surely deliver thee from all sin and evil; do not grieve.” At the end, the flickerings of faith will cease; for we shall see his face and feel always the Divine Presence.
Ref : The Synthesis of Yoga