Verses 25 and 26 form one sentence in Greek, but Good News Translation breaks in into two shorter sentences to produce a clearer rendering. Since in Greek there is no punctuation mark after I am sure of this, it is possible to interpret this phrase in two different ways. (1) It is sometimes taken adverbially to modify the following verb I know, thus with the meaning “of this I am confidently persuaded,” or “this I know confidently.” New English Bible appears to favor this interpretation with “this indeed I know for sure.” This would then refer to I will stay. (2) However, several translations (Good News Translation Revised Standard Version Goodspeed Moffatt etc) understand the clause to refer to the preceding verses. That is to say, Paul is sure that to stay alive for his Philippian friends’ sake would be his duty if the choice were left to him, because he is convinced that his remaining would be for their good. On the basis of this interpretation, it may be necessary to translate “I am sure that I would choose to continue to live.”
I know reflects Paul’s personal conviction. This conviction is vividly expressed by employing a play on words. The verb rendered stay on is a compound of the simple verb translated stay. It means to stay or wait beside a person, so as to be ready to help and to serve (New English Bible “I shall stay, and stand by you all to help”; Goodspeed “I shall stay on and serve you all”). A literal rendering of I will stay on with you all can be misinterpreted, since it may seem to imply that Paul would continue to stay with the Philippians for some period of time. It may therefore be useful to translate this clause as “I will continue to live and to help you all.” In a sense, this anticipates the final clause of the verse.
To add to your progress and joy in the faith is literally “into your progress and joy of the faith.” Here “into” has the force of to add (Goodspeed “to help”). Progress and joy share one article, so they should probably be taken closely together with faith. Phillips appears to miss the point in taking them to mean two separate ideas: “to help you forward in Christian living and to find increasing joy in your faith.” On the other hand, it seems unnecessary to take them so closely together as to merge them into a single idea as Knox does: “happy furtherance.” Progress is the same word used in 1.12, but here it applies to the progress of the Philippians’ faith. The word faith here stands for experience based on trust in God and on Christ and his redeeming work. For Paul, joy is an indispensable element of that experience.
Despite the close association of progress and joy, it may be necessary to dissociate them in view of their relation to the verb add to and the final purpose, namely, the faith. In the first instance, it may be necessary to translate “so as to cause you to have more and more faith.” The final expression, dealing with joy, may then be rendered as “to cause you to have more happiness in your faith,” or “… as you trust Christ.”
Quoted with permission from Luo, I-Jin. and Nida, Eugene A. A Handbook on Paul’s Letter to the Philippians. (UBS Handbook Series). New York: UBS, 1977. For this and other handbooks for translators see here .