How frustrating for Paul to be challenged on the same information 3 times. He was also being questioned as to whether or not he was being used by God to deliver his message. Paul still humbles himself by letting them know that he too is weak yet strong through Christ. He has pulled all stops to get them to follow. Now I understand his frustration. Raising my girls brought out the same frustrations as we as parents would, with good intention, present them with our insight as to which way to go in life. However I do not think we met with nearly the same resistance as these disciples did.
Ah! examine ourselves. Great idea. I do not think I do that enough. Paul is asking them to perform an examination letting them know that if they find they are strong Jesus is in them. If they are not, he is absent. After all his teaching He wants to rest in the knowledge that even though he may feel he has failed that the people have in fact heard the word of God and have been built up. Paul makes it clear he does not want to have to return and be harsh in his dealings with them.
Now after all this worry, Paul leaves them with the most loving of instructions. He tells them that with all this new found blessing to REJOICE. He tells them to restore and encourage one another, be of one mind and live in PEACE. May we all listen to Paul's words and take this Godly advice. We will then receive the blessings of God, a life of peace and joy only given to the believer who loves and seeks after our amazing Lord.