In the Sermon on the Mount, Jesus says to “take no thought for your life, what ye shall eat” (Matt. 6:25). He is talking about physical life and physical food, and the obvious relationship between the two. He is telling us not to chase after our physical lives in the first instance, and that chasing after food is the way that this would be done.
In another place, He tells us that He offers Himself as living bread (John 6:51) Unless we partake of this living bread, we have no life in ourselves (John 6:53). Just as physical life is sustained by physical food, so also spiritual life is sustained by spiritual food.
We cannot get nourishment from food when the nourishment is not there, which is why we cannot eat rocks or plastic. We can eat fruit, and meat, and vegetables, and they offer up what they contain. But they don’t transmit what they contain automatically, no matter what we do. Smearing food on our foreheads is not eating.
In the New Jerusalem, we are invited to eat from the tree of life (Rev. 2:7). This means that the fruit is life, and that we get to chew and swallow life. We eat, and take life into ourselves. We do this because Christ is life itself. But you cannot come to this Table, you cannot come to church and get blessing from it regardless of your behavior. If you take the life that is here and smash it on your forehead, you are not eating. And since this is spiritual food and drink, the warning has to be against smearing food on your spiritual forehead. That is not where your mouth is.
What is your spiritual mouth? It is your faith. And just as the food is living, so must the mouth be. As God has quickened you, and given you a true and living faith, then come, and welcome to Jesus Christ.