Cleansing one's thoughts is eminently more spiritually important than washing one's hands.
An often-misunderstood passage is Mark:7:18-19. Here Jesus said: "Do you not perceive that whatever enters a man from outside cannot defile him, because it does not enter his heart but his stomach, and is eliminated, thus purifying all foods?" The subject here—made obvious from verses 2-5—was ceremonially unwashed hands, not which meats could be eaten. The purification of food referred to the way the body's digestive process eliminates minor impurities such as those that might be present from eating with unwashed hands.
The Pharisees, like Jesus and His disciples, ate only meat the Scriptures specified as clean. They objected, however, when Jesus and His disciples did not go through the Pharisees' customary ritual of meticulously washing their hands before eating.
Jesus, whose hands were sufficiently clean for eating even if not clean enough to meet the Pharisees' humanly devised standards, explained that the human body was designed to handle any small particles of dust or dirt that might enter it due to handling food with hands that hadn't been ritually washed.
He further suggested that, if the Pharisees were serious about wanting to obey God, they needed to revise their priorities. Cleansing one's thoughts, He said, is eminently more spiritually important than washing one's hands (verses 20-23).
The New International Version of the Bible renders the latter part of verse 19: "(In saying this, Jesus declared all foods Ôclean.')" The New American Standard Bible similarly offers: "(Thus He declared all foods clean.)" These translations stand in stark contrast to the King James and New King James versions, which indicate that the bodily digestive process purifies food as opposed to Jesus making a pronouncement reversing God's laws on which meats to eat. The New King James Version says that whatever comes into a man's body from outside "does not enter his heart, but his stomach, and is eliminated, thus purifying all foods" (verse 19). Which interpretation is correct?
The King James and New King James renditions best fit the context, which concerns eating with ceremonially unwashed hands rather than deciding which kind of flesh is suitable to be eaten. They also best fit the New Testament culture wherein Jews and Christians ate only clean meats.
In the original Greek the words "In saying this, Jesus declared" (NIV) and "Thus He declared" (NASB) are not present; translators have added them to explain what they think Mark intended and as a result have placed their own preconceived and mistaken interpretations on Jesus' words.
For More Information, see What Does the Bible Teach About Clean and Unclean Meats?