I protest - (νὴ nē). This is a particle of swearing, and denotes a strong asseveration. The subject was important; it deeply interested his feelings; and he makes in regard to it a strong protestation; compare John 3:5. “I solemnly affirm, or declare.”
By your rejoicing - Many manuscripts here read “by our rejoicing, but the correct reading is doubtless that which is in the present Greek text, by your rejoicing. The meaning of the phrase, which is admitted by all to be obscure, is probably, “I protest, or solemnly declare by the glorying or exultation which I have on your account; by all my ground of glorying in you; by all the confident boasting and expectation which I have of your salvation.” He hoped for their salvation. He had labored for that. He had boasted of it, and confidently believed that they would be saved. Regarding that as safe and certain, he says it was just as certain that he died daily on account of the hope and belief of the resurrcction. “By our hopes and joys as Christians; by our dearest expectations and grounds of confidence I swear, or solemnly declare, that I die daily.” People swear or affirm by their objects of dearest affection and desire; and the meaning here is, “So certainly as I confidently expect your salvation, and so certainly as we look to eternal life, so certain is it that I am constantly exposed to die, and suffer that which may he called a daily death.”
Which I have in Christ Jesus - The rejoicing, boasting, glorying in regard to you which I am permitted to cherish through the grace and favor of the Saviour. His boasting, or confident expectation in regard to the Corinthians, he enjoyed only by the mercy of the Lord Jesus, and he delighted to trace it to him.
I die daily - compare Romans 8:36. I endure so many sufferings and persecutions, that it may be said to be a daily dying. I am constantly in danger of my life; and my sufferings each day are equal to the pains of death. Probably Paul here referred particularly to the perils and trials which he then endured at Ephesus; and his object was to impress their minds with the firmness of his belief in the certainty of the resurrection, on account of which he suffered so much, and to show them that all their hopes rested also on this doctrine.