Evidences

2 Corinthians 3:4-5
And such trust have we through Christ to God-ward:
Not that we are sufficient of ourselves to think any thing as of ourselves; but our sufficiency is of God;
Paul had defended his ministry by saying that the results of his ministry were sufficient evidence that his ministry was of God.
Those who had been saved
Those churches that had been founded
Those who had come to follow Christ through his preaching
Those were the "letters of commendation" for his ministry.

But then Paul said that even that was not the primary focus of his ministry.
His sufficiency
His faith
His confidence
Was not even dependent upon the results of his ministry. His sufficiency was entirely of God.

When a person walks with God there will be fruit naturally produced. This fruit is a sweet reward and commendation of our walk, but it should not be considered essential or necessary to maintain our walk. Knowing Christ is sufficient when we truly know Christ.