The mind tells you "it can't be done"; the Spirit says that with God all things are possible. The mind says you surely won't get what you need; the Spirit says your Father knoweth what things you have need of and they will be supplied out of His riches in glory. In this way, the negative and depressing thoughts of the mind are commanded out, and are replaced with the positive promises of God's Word. The mind is an instrument in our hands. We must command it.