But when the Spirit Himself is the interpreter of those things which He suggests, then there can be no doubt about outcome and certitude. You will find nothing like this in the dreams of the heathen except that keen disturbance of the heart. But because they have Satan as their author, who can and is accustomed to give reminders of future events, they are generally ambiguous and deceptive, and no interpreter is provided, as is the case in dreams from God which the prophets report with certainty and faithfully, with the Holy Spirit as their teacher. From the dreams sent to them, Daniel, Jacob, and Joseph gather the doctrine and meaning of Holy Scripture concerning very important matters, not only concerning the empires which they taught were established and preserved by God but also concerning the kingdom of Christ and the chief articles of Christian doctrine. Therefore it depends on a good interpreter! A good interpreter is required, as we say in the German proverb.
Luther’s works, vol. 6: Lectures on Genesis: Chapters 31-37 p 332