The following is one of my favourite quotes. It comes from The Ministry of Healing, p. 250:
When temptations assail you, when care, perplexity, and darkness seem to surround your soul, look to the place where you last saw the light. Rest in Christ’s love and under His protecting care. When sin struggles for the mastery in the heart, when guilt oppresses the soul and burdens the conscience, when unbelief clouds the mind, remember that Christ’s grace is sufficient to subdue sin and banish the darkness. Entering into communion with the Saviour, we enter the region of peace.
This encouragement has carried me through many a dark and troubled time in my life.