In the opening of the letter to the Philippians, Paul mentions how grateful he is of the believers at Phillipi in "view of their participation in the gospel" (1:5).

What exactly is "participation in the gospel"?

In verse 7 Paul mentions "the defense and confirmation of the gospel"; defense is probably clear to us and has the idea of defending Christ and His work from unbelivers or those who twist and distort the truth.  But what is "confirmation of the gospel"?

Paul continues by praying that their "love may abound" (1:9) in real knowledge and discernment, approving the things which are excellent, in order to be sincere and blameless until the day of Christ (1:10); having been filled with the fruit of righteousness which comes through Christ. (1:11)

So the "confirmation of the gospel" is a life of love, rooted in real knowledge; a life which has the fruit of righteousness which comes through Christ.  We defend the gospel with our minds and words, and we confirm the gospel with our mind, heart and actions.

It is completely the work of God. (1:6, 11)