'If also' and 'if even' (twice) in this verse represent the same Greek expression. The first is translated 'if also,' which, while literal, is more delicate, as expression of feeling, than 'though.' 'If even' would here express an extreme case or doubt; 'also' is admitting an additional fact. Hence I put 'if even' for the other cases in the sentence. In the second case he suggests in the way of admission, as the extreme to which he went, i.e. regret: he was right and inspired, but felt the distress individually, and would not leave them ignorant of how far his love went; so in the third case it is the same limitation of their grief. 'Ye were sorry, if even it were only for a time.'
Or perhaps 'for the sake of our diligent zeal for you before God being manifested to you.' The reading is uncertain here. It is possible that the true reading is 'your zeal for us.' Its force then would be, 'that you might discern how truly you loved us, though turned aside by false teachers.' Compare ver. 7.
'The rather ... more abundantly.' This is a common Greek idiom, but it is impossible to render it exactly in English. The A.V. translates the expression 'exceedingly the more,' but in English 'the more' supposes more than something, and because of something. I do not think it always merely emphatic; there is an unexpressed motive which is the cause of 'the rather' in the mind. I suspect that ver. 14 gives the clue to the force of it.
It may, perhaps, be translated 'and in (or 'besides') our encouragement we the rather rejoiced more abundantly in the joy of Titus (for his spirit is refreshed by you all), because if I,' &c. There are often examples of the change of 'I' and 'we' in this epistle; it is the case in this very context. But not without a reason in the sense, 'I' being more personal to Paul.