Every believer has their own convictions in life. Some have found complete freedom in Christ while others continue to wrestle with certain things. Paul gives instruction to both types of believers to accept and encourage each other without passing judgment.
The example he used was the difference between Jewish believers and Gentile believers. The Gentiles had no convictions about eating certain meats but the Jewish Christian would only eat vegetables for fear of breaking an Old Testament dietary law. Paul said that the Gentile Christians should not look down on the Jewish Christians because their faith had limited their diet. In the same way the Jews should not condemn the Gentiles for eating those meats and exercising their freedom in Christ.
Paul is revealing the danger for those who have a revelation of God's grace; it is easy to become insensitive to and impatient with brethren who haven't yet come to that knowledge. We must learn to balance our freedom in Christ around those brothers and sisters so we can encourage and love them without destroying them in the process. In the same way, believers that haven't yet renewed their mind to this freedom can become judgmental and condemning of other brothers. They also need to consider that God has accepted their brethren and shown them the freedom to which they were called. Each person should consider one another and how to mutually edify and encourage in the Lord instead of condemning and destroying.
As such we were called to be servants, not judges. We have a responsibility to judge ourselves alone and let the Lord judge others. We should make sure that we put no stumbling blocks in anyone's way. We should be fully convinced in our own minds what is right and good to do and act upon that. If we do this, then we are proceeding in faith and the Lord responses to faith. Paul said later on in this chapter, "everything that does not come from faith is sin" ( Romans 14:23 ). Therefore we should let the Lord reveal these truths to us and act on them alone without condemning our brothers and sisters who haven't yet come into this revelation. For the Lord is mighty to support and uphold us, He is patient as we walk further and further into the knowledge of His word.
May God bless you with a revelation of the freedom that was purchased for you in Christ Jesus and may you walk in this, fully convinced in your heart, amen!