"Therefore judge nothing before the appointed time; wait till the Lord comes. He will bring to light what is hidden in darkness and will expose the motives of men's hearts. At that time each will receive his praise from God." NIV translation
We, as people, do not have all of the facts as we cannot see into the minds and hearts of others but God can and does. Paul reminds the believers (and us as well) to reserve judgment until all is revealed by Jesus Christ. For example, we may see a man doing drugs and want to condemn him for doing them but we do not see that the desire of his heart is to be free from the bondage of drug addiction. God knows his heart and therefore shows him compassion. We are to do the same and to tell him how he can overcome the addiction and be set free.
"Now, brothers, I have applied these things to myself and Apollos for your benefit, so that you may learn from us the meaning of the saying, 'Do not go beyond what is written.' Then you will not take pride in one man over against another. For who makes you different from anyone else? What do you have that you did not receive? And if you did receive it, why do you boast as though you did not?" NIV translation
Paul was a humble man and lets the people know that he is not just talk but applies the word to his life as well. He had been proud of his knowledge of Jewish law but, he had received the revelation of Christ, not through any teaching of man but directly from Jesus. What do you have that you take pride in? A house or car or family or job? Those, too, are from God and He is watching to see if you give Him the credit and how you use them for His kingdom.
"Already you have all you want! Already you have become rich! You have become kings - and that without us! How I wish that you really had become kings so that we might be kings with you!" NIV translation
The people that Paul is talking to have gained earthly wealth and power but have forgotten that God gave it to them. They also forgot that He gave it to them for a purpose and that purpose is not building up their own personal earthly kingdom. To really be kings (as seen in Revelation 20), we must remember that Jesus is the head of the kingdom.