I found Philemon verse 6 a bit of a mouthful and hard to understand. Scholars say the Greek is very hard to translate into succinct English. So I thought I would present some research to help us understand. 

Translations:

(ESV) and I pray that the sharing of your faith may become effective for the full knowledge of every good thing that is in us for the sake of Christ.

(NIV) I pray that your partnership with us in the faith may be effective in deepening your understanding of every good thing we share for the sake of Christ.

(NASB) and I pray that the fellowship of your faith may become effective through the knowledge of every good thing which is in you for the sake of Christ.

(CSB) I pray that your participation in the faith may become effective through knowing every good thing that is in us for the glory of Christ.

Comment:

Alistair I. Wilson writes, “These translations appear to agree that Paul prays that the common faith he and Philemon share will be seen in the growing appreciation of the remarkable nature of what God has accomplished for those who are united to Jesus by faith.” Paul’s emphasis is more so on ‘the communion / the fellowship / the participation in the Faith’. Hence, the ESV’s translation “the sharing of your faith” should not be interpreted as a reference to evangelism. With the shared goal of fellowship, whenever someone enters into the participation of the faith, they will become strengthened by acknowledging blessing from Christ in their community.

“By the acknowledging”: As the recipients and witnesses of Philemon’s goodness saw more and more clearly the motive and spirit of it, they would have a truer insight into the power of the Gospel. Experiencing goodness from Philemon, believer’s could accredit that to Christ. A knowledge “which, in such pious fellowship, unfolds itself ever more fully and vividly, and which must be the means of powerfully promoting all Christian activity” (Meyer’s NT Commentary).

“Every good thing”: every grace, the gift of love in all its practical manifestations. That this fellowship becomes effective when all believers acknowledge the goodness of God in them and among them.

Application:

Christian fellowship is effective when acknowledgement/credit that all good things in/around them are from Christ. As Paul prays for Philemon, he encourages the Christian fellowship to be a means where he will understand and see God’s goodness, but also to put into practice this good that God wills, and to do all this for the sake of Christ. In other words, faith is seen in the appreciation of the good things God has done for those who are united in Christ, and to actively participate in doing good for fellow believers. 

Ashleigh