Philippians 1:25

‘And having this confidence, I know that I will abide, yes, and abide with you all, for your progress and joy in the faith,'

So the bitter struggle is resolved for him by the recognition of their continuing need of him. That is why he is confident that he will continue living in this world, and will do so in a way which enables him to live continually among them, both so as to ensure their progress in Christ, and to stimulate their growing and continuing joy in Christ and in His Gospel (compare Acts 13:52). His whole desire is for what will be for the greatest benefit of both Christ Himself and of His church.

‘Progress and joy --.' The first emphasises his desire for their advancement as they move forward to new things, the second has in mind the quality of their spiritual lives. He wants them both to grow, and be qualitatively blessed in that growth.