In his farewell address to the Israelites, Moses warns the people not to allow their hearts to be deceived, lest they go after false gods. This statement in and of itself is so contrary to the pop psychology of the day: follow your heart. When people are in decision-making moments in life, the advice often given is to ask the question, "What does your heart tell you?" Moses taught, and experience proves, that the heart is deceitful: the heart cannot always be trusted.
So how do you ensure that you are not deceived? Store God's Words in your heart. Memorize them, tell them to your children, bind them to your foreheads so they do not leave your presence. You will not be deceived if you know God's Word because you will be able to spot false religion from a mile off. How are you doing at guarding your heart against deceit?