Delusion: an erroneous or invalid belief or opinion. The initial intellectual error from which all other delusions and their consequences result is presuming the true Self (the soul) to be mind or matter.
January 12th The Meaning of Life
The devotee should understand that the purpose of God in creating the world and Delusion is to develop perfect beings. This pastime is God's hobby! To encourage perfection, the Lord gave men free will — and a challenge! He subjected them to the inner wholesome temptations of His goodness and to the outer unwholesome temptations of Nature. Human life is a vast complicated puzzle that each man must solve to the last. When man skilfully uses his divine gift of free choice and discrimination to respond to the temptations of virtue and not of evil, he attains the necessary victory. He is 'out' in the game of life; he returns to his blessed Home with heavy winnings! This then, is the truth about the mystery of human life on earth. This is the reason why man should not yield (as many psychologists wrongly advise) to the 'natural' impulses, but should be guided by spiritual inclinations that are truly natural to his being, the soul.
—Sri Paramahansa Yogananda, God talks with Arjuna: the Bhagavad Gita - Royal Science of God-realization