2 Corinthians 3

Paul's verification of his ministry did not come from a letter of recommendation or self-promotion. It came from the Corinthians themselves. They knew what he had done among them during his time with them. Paul rested in the knowledge of that work - he did not need "independent verification" of his ministry. The 'cloudiness' over the understanding of some was not because of Paul's qualifications but due to the spiritual ignorance some had because of their spiritual deadness. Those who enjoy a relationship with the Lord, have the Holy Spirit dwelling within them and transforming them into knowledgeable and God-pleasing people.