Specific Text - Mark 7:1-23
The Pharisees were so concerned with not violating God's laws that they developed an entire system of secondary laws to form a hedge. The idea was that adhering to this additional set of rules would help ensure that they never got anywhere close to violating God's law. The big problem with this plan is that temptation comes from inside of you, not from the outside. In the case of the Pharisees, this secondary system of laws and customs meant to keep them on the path of righteousness turned into a god for them to serve, and rather than protecting them, it caused them to break the first commandment.
We also have many Christian traditions and customs that, when done correctly, help keep us from getting into deeper trouble. Jesus is not condemning these practices, but He wants to make sure that you understand that just following external rules will do nothing to solve your ultimate problem.
Your ultimate problem is that you are addicted to sin. Jesus is saying here that because your heart is filthy, it doesn't matter how clean you keep your hands... you need to get your heart fixed first, and your heart needs to be cleaned from the outside. This is the opposite direction most people go in. Most people search the world over looking for ways to fix themselves from the inside: they try all sorts of religious practices, meditation, and a host of other strategies, but nothing you try to do yourself will work. It's like trying to clean your heart with dirty water.
Jesus here is teaching you that since you can't fix yourself from within, you need to rely on something from the outside. Nothing in this world will work however, since it's all corrupted by sin - it's all dirty water. What you need is something that comes from outside of creation... you need the Holy Spirit, who connects you through faith to the person and work of Jesus Christ.
Prayer for the day: Dear Father in heaven, help me to realize how sinful my heart is. Thank you for sending your Spirit to me to take my sin and replace it with the perfectly clean righteousness of your Son, Jesus Christ. In His name I pray, Amen.