"Make every effort to live in peace with everyone and to be holy; without holiness no one will see the Lord." NIV translation
How do we live in peace with everyone? It is only possible through Jesus Christ and remembering our place. The previous section spoke of how God is the one that disciplines Christians and, if we remember that, we will not have all of the struggles and strife between believers. Paul goes on to remind us that our goal in this life is to be holy which means that God is in control of our lives. We have confused our holiness with the concept of being sinless but they are not the same. If we are in Christ and listening to the Spirit, then, God will correct us as needed.
"See to it that no one falls short of the grace of God and that no bitter root grows up to cause trouble and defile many." NIV translation
We are warned of the dangers of falling into a pattern of legalism. Falling short of the grace of God is not talking about sinning it is talking about trying to add works to grace for salvation. When we do so, we start to judge the salvation of others and that produces division in the body of believers. That is the bitter root that Paul is speaking about.
"See that no one is sexually immoral, or is godless like Esau, who for a single meal sold his inheritance rights as the oldest son. Afterward, as you know, when he wanted to inherit this blessing, he was rejected. Even though he sought the blessing with tears, he could not change what he had done." NIV translation
We are reminded of the story of Esau selling his birthright for a bowl of soup (see Genesis 25). Esau was a man of the flesh and did not even care about spiritual matters. God uses the Spirit to guide and correct His children but a man that is not concerned with spiritual matters cannot be disciplined. The tears that Esau shed were not of repentance but were sadness and a desire to get the material blessings that he lost. He still did not have the desire to be restored in his relationship with God.