The concept of what defiles a man is primarily derived from the teachings of Jesus Christ, as recorded in the New Testament. This topic addresses the nature of purity and impurity, focusing on the internal rather than external aspects of human behavior and spirituality.

Biblical Context

The primary scriptural reference for understanding what defiles a man is found in the Gospel of Matthew and the Gospel of Mark. In Matthew 15:10-20 and Mark 7:14-23, Jesus addresses the Pharisees and the crowd, challenging the traditional Jewish emphasis on ritual purity and dietary laws.

Matthew 15:10-20 :
"Jesus called the crowd to Him and said, 'Listen and understand. A man is not defiled by what enters his mouth, but by what comes out of it.' Then the disciples came to Him and said, 'Do You know that the Pharisees were offended when they heard this?' But Jesus replied, 'Every plant that My heavenly Father has not planted will be pulled up by its roots. Leave them; they are blind guides. If a blind man leads a blind man, both will fall into a pit.' Peter said to Him, 'Explain this parable to us.' 'Do you still not understand?' Jesus asked. 'Do you not yet realize that whatever enters the mouth goes into the stomach and then is eliminated? But the things that come out of the mouth come from the heart, and these defile a man. For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false testimony, and slander. These are what defile a man, but eating with unwashed hands does not defile him.'"

Mark 7:14-23 :
"Once again Jesus called the crowd to Him and said, 'All of you, listen to Me and understand: Nothing that enters a man from the outside can defile him, but the things that come out of a man, these are what defile him.' After Jesus had left the crowd and gone into the house, His disciples inquired about the parable. 'Are you still so dull?' He asked. 'Do you not understand? Nothing that enters a man from the outside can defile him, because it does not enter his heart, but it goes into the stomach and then is eliminated.' (Thus all foods are clean.) He continued: 'What comes out of a man, that is what defiles him. For from within the hearts of men come evil thoughts, sexual immorality, theft, murder, adultery, greed, wickedness, deceit, debauchery, envy, slander, arrogance, and foolishness. All these evils come from within, and these are what defile a man.'"

Theological Implications

The teachings of Jesus in these passages emphasize the importance of the heart's condition over external observances. The Pharisees, known for their strict adherence to the Mosaic Law, focused on ceremonial cleanliness and dietary restrictions. Jesus, however, redirects the focus to the moral and spiritual state of an individual. He asserts that true defilement is a matter of the heart, where evil intentions and sinful behaviors originate.

This teaching underscores the principle that righteousness is not achieved through external compliance with religious rituals but through the transformation of the heart. The internalization of God's commandments and the cultivation of a pure heart are central to living a life pleasing to God.

Practical Application

For believers, this teaching calls for introspection and a focus on inner purity. It challenges individuals to examine their thoughts, intentions, and actions, recognizing that these are the true indicators of one's spiritual state. The emphasis is on cultivating virtues such as love, honesty, and humility, which reflect a heart aligned with God's will.

In summary, the biblical teaching on what defiles a man shifts the focus from external rituals to the internal moral and spiritual condition, highlighting the significance of the heart in determining true purity before God.