Jamieson, Fausset and Brown on Philippians 1:10

10. Literally, "With a view to your proving (and so approving and embracing) the things that excel" (Ro 2:18); not merely things not bad, but the things best among those that are good; the things of more advanced excellence. Ask as to things, not merely, Is there no harm, but is there any good, and which is the best?

sincere--from a Greek root. Examined in the sunlight and found pure.

without offence--not stumbling; running the Christian race without falling through any stumbling-block, that is, temptation, in your way.

till--rather, "unto," "against"; so that when the day of Christ comes, ye may be found pure and without offense.