John Calvin on Philippians 1:5

5 For your fellowship. He now, passing over the other clause, states the ground of his joy — that they had come into the fellowship of the gospel, that is, had become partakers of the gospel, which, as is well known, is accomplished by means of faith; for the gospel appears as nothing to us, in respect of any enjoyment of it, until we have received it by faith. At the same time the term fellowship may be viewed as referring to the common society of the saints, as though he had said that they had been associated with all the children of God in the faith of the gospel. When he says, from the first day, he commends their promptitude in having shewn themselves teachable immediately upon the doctrine being set before them. The phrase until now denotes their perseverance. Now we know how rare an excellence it is, to follow God immediately upon his calling us, and also to persevere steadfastly unto the end. For many are slow and backward to obey, while there are still more that fall short through fickleness and inconstancy. “Qui se reuoltent ou defaillent en chemin par legerete;” — “Who revolt or fall back in the way through fickleness.”