'Simplicity' here refers, not to a personal trait, but to the doctrine as to Christ; what a faithful heart retained in simplicity, as taught in the truth. To say 'which [is] in the Christ,' is too much as if it were in Christ himself, not the doctrine.
The word here translated 'above measure' is so used constantly by the apostle, though not indeed separated from the word it refers to. But I do not find that it is used adverbially for 'more than;' and the expression 'as being beside myself' seems to refer to the extra-ordinariness of what he was saying, for he felt that to say 'minister of Christ' was to say all that was excellent. Hence he does not repeat 'in folly,' but says 'as being beside myself,' 'wandering quite away from a right mind.' His own heart did not allow him to say he was 'minister of Christ' without judging the expression, though forced to use it for these foolish Corinthians. The word translated 'exceedingly abundant' is not really a comparison, and the words translated 'to excess' and 'oft' show that no comparison with others is instituted. He left his miserable competitor far behind, and his soul turned back with true heartfelt satisfaction to all he had undergone for Christ. His folly is given to us for gain by God. However, if anyone prefer 'more than they' or 'beyond them' to 'above measure,' in result the sense is not altered, though, it seems to me, feebler and more disjointed.
See same words in 1Thess. 2.9; 2Thess. 3.8.
'Burden' here means any solicitude or anxiety, but 'care' misleads, because it conveys the idea of taking care of, which is not the sense. Same word as 'anxious care,' Matt. 13.22, and 'care,' 1Pet. 5.7.