Only conduct yourselves in a manner worthy of the gospel of Christ, so that whether I come and see you or remain absent, I will hear of you that you are standing firm in one spirit, with one mind striving together for the faith of the gospel; in no way alarmed by your opponents--which is a sign of destruction for them, but of salvation for you, and that too, from God. For to you it has been granted for Christ’s sake, not only to believe in Him, but also to suffer for His sake, experiencing the same conflict which you saw in me, and now hear to be in me.
Calvinists infer Irresistible Grace, but where does the context imply anything irresistible? This is about God granting the privilege of believing in Him and suffering for Him, which is also reminiscent of God granting repentance to the Gentiles (Acts 11:17-18), and God granting repentance to those in opposition. (2nd Timothy 2:24-26)
John Calvin comments: “Here Paul clearly testifies that faith, as well as constancy in enduring persecutions, is a free gift of God.” (Calvin’s New Testament Commentaries: Galatians, Ephesians, Philippians and Colossians, p.243, emphasis mine)
Actually, faith is received from hearing the Gospel. (Romans 10:17) A better way to understand this is to see if through the lens of God bringing them the message of “the Gospel of Christ” so that they can believe in it, and become saved, and even further, to serve God through tribulations caused by those in opposition. That seems to be a more reasonable interpretation, than importing a TULIP system with Irresistible Grace.
Laurence Vance comments: “The verse in Philippians is cited by Calvinists when seeking to prove that faith is God’s gift to his ‘elect’ so they can have their Total Depravity overcome by Irresistible Grace. But since not all Christians ‘suffer for his sake,’ an irresistible gift could not be in view.” (The Other Side of Calvinism, p.344)