Athanasius of Alexandria — on 1Tim 4:7 (FESTAL LETTERS 10.3)

“Therefore St. Paul urges us to exercise our faith in the face of troubles. Having already come through them victoriously, he said, "Therefore I take pleasure in persecutions and weaknesses." In another place he said, "Exercise yourself in godliness." He knew that those who choose to live godly lives are going to be persecuted, so he wanted his disciples to be aware of the difficulties they would face. Then when the trials and afflictions did come, they would have built up enough strength to handle them easily. You yourself know that when you've been looking forward to something, even if it's hard, you experience a secret joy when it actually comes.”