Paul now goes on to define the purpose of his prayer in verse 9. The same Greek expression translated to choose what is best appears also in Rom 2.18, where Good News Translation renders it as “to choose what is right.” The Greek term here translated to choose is sometimes used in the technical sense of testing coins to determine whether they are genuine. Thus the Good News Translation rendering carries the force of accepting or choosing what is proved to be right or best or essential in religion (Moffatt Goodspeed “to have a sense of what is vital”; New Engish Bible footnote “may teach you by experience what things are most worthwhile”). The phrase what is best means literally “things which differ” or “things that excel.” The latter meaning seems to suit the context better. It is a reference to the ability, not so much to distinguish right from wrong or good from bad, but to determine what is best among all that is good.
What is best is a general qualification which it is not always possible to employ. Certainly it is not a reference to particular things or objects, but rather to behavior and experience. It may be necessary to render the first part of verse 10 as “so that you will be able to choose what is best to do,” or “… how you should best behave.”
Then you will be free from all impurity and blame on the Day of Christ (literally, “so that you may be pure and blameless with a view to the Day of Christ”) is taken as the result of having the ability to discriminate what is best. The adjective rendered free from all impurity occurs elsewhere in the New Testament only in 2 Peter 3.1. It means “unmixed,” “genuine,” or “unadulterated.” It may be rendered in some languages as “not having anything bad about you,” or “without any wrong.” The adjective translated free from … blame can mean either “not causing others to stumble” or “not stumbling.” Paul seems to have in mind the fitness of the Philippians to stand before Christ on the Day of judgment. In this context it is better to adopt the meaning of “blameless.” This concept may be expressed in some languages as “without having done anything for which you could be blamed,” or “without having done what was wrong.”
On the Day of Christ, as in Pp. 1.6, refers to the Parousia, so it is possible to render it more explicitly as “on the Day when Christ comes back.”
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 .