“It is not what goes into the mouth that makes a person unclean. It is what comes out of the mouth that makes a person unclean” (Matthew 15:11)
Yes, Jesus says that in Matthew 15:11 and in Mark 7:15 in response to the Pharisees accusing his disciples of being defiled because they ate with unwashed hands. The point Jesus was making with this statement is that the Pharisees placed greater importance on their own traditions than they did on following God’s instructions and that it is their lack of acknowledgement of God’s instructions that defiles them.
So even though it had nothing to do with justifying which kinds of food are acceptable to eat, let’s assume for the sake of argument that it did and that we are seeking to base our dietary decisions on it. What logical conclusion would that lead us to?
If you say you do everything in love (as it says to do in 1 Corinthians 16:14), yet your attitude and actions toward animals suggest anything but love, then what is coming out of your mouth are lies and it is those lies that defile you.
God is love (1 John 4:16) and his word is truth (John 17:17). The devil is the father of lies (John 8:44). We should be very careful not to forsake love in favor of serving the desires of the flesh (Philippians 3:19). And we should be just as careful not to cover up what we are doing with lies the way David twice tried to cover up his affair with Bathsheba (2 Samuel 11). Instead we should confess our mistakes and turn away from them (Proverbs 28:13; 1 John 1:9). We should love mercy (Micah 6:8) rather than the bloodthirsty appetites of the flesh (Galatians 5:24).