In the spiritual sense, "eating" occurs primarily when one hears and reads. A person ingests messages and concepts into the mind through words, which establish and nourish his pattern of life. Those words, if one permits it, create a faith upon which one bases the way he lives. This faith is almost entirely dependent upon the quality of what is heard and whether a person believes it enough to follow it. These verses reveal that only the words of God or Christ, His gospel, His truths, will form the faith that leads to salvation because they will form the correct beliefs and thus the correct way of life. This is the faith of Christ; the person who has it believes what Christ believes. This is a simple, understandable, true formula.
Zephaniah 3:1-2 shows what happens when a person rejects or disbelieves His words: "Woe to her who is rebellious and polluted, to the oppressing city! She has not obeyed His voice, she has not received correction; she has not trusted in the LORD; she has not drawn near to her God." That person comes to great dismay. This does not mean we cannot have words other than God's in our mind, but the children of God must filter everything through God's words to test their validity before they allow themselves to believe them firmly enough to make them part of their belief system.
Put another way, there is faith and then there is the faith, the faith that brings salvation. This faith arises from believing God's words. What we believe will determine our conduct and attitudes whether or not we stop to think about those beliefs because what is contained in the heart will come out (Matthew 12:34-35). Only God's words truly produce spiritual strength. In our recent past, "eating" and believing the wrong words set the church up for the scattering that has occurred. For quite a while, worldly things gradually corrupted the spiritual health of God's children, weakening them through spiritual malnourishment and changing their faith.
I Corinthians 1:10 provides a first-century account of a congregation suffering from this process of ingesting the wrong words: "Now I plead with you, brethren, by the name of our Lord Jesus Christ, that you all speak the same thing, and that there be no divisions among you, but that you be perfectly joined together in the same mind and in the same judgment." Division troubled this congregation because the members held dissimilar views on beliefs that are basic to spiritual unity. I Corinthians shows disorder, confusion, argument, and offense as symptoms of spiritual weakness.