And not frightened in anything by your opponents. This is a clear sign to them of their destruction, but of your salvation, and that from God.
1:28 – Here, Paul notes what it is that the community ought to be striving together for – i.e., courage in spite of opposition. Whether this was already occurring in the Philippian community or not, one cannot not positively deduce, but it is apparent that Judaizers had some domineering presence in Philippi (cf. 3:2). The certainty, however, is that the persecution for believers is real, and ought to be met with boldness and courage. How can they not be frightened by their opposition? What are the grounds for their steadfast courage? If you find yourself in opposition, you can have courage because of these reasons:
1) It is a sign of salvation to us. It is similar to what Paul asserted concerning his opposition and trial (1:19); this is directly working out as an assurance of their salvation. The foundation of Christian boldness is faith, which is the substance of a soteriological hope. Nothing can shake your citizenship. Your salvation is locked in by the faithfulness of God and His reckoning, and the struggle is not stronger than Him. There is also some hint of the undeniable persecution that comes with being a Christ follower (cf. Matthew 5:10; Luke 6:22; John 15:18-19; 2 Timothy 3:12; 1 Peter 3:14). Thus, it is a valid deduction that Christians are promised persecution, whereby persecution signifies their Christianity. ‘Beloved, do not be surprised at the fiery trial when it comes upon you to test you, as though something strange were happening to you. But rejoice insofar as you share Christ’s sufferings, that you may also rejoice and be glad when his glory is revealed. If you are insulted for the name of Christ, you are blessed, because the Spirit of glory and of God rests upon you…However, if you suffer as a Christian, do not be ashamed, but praise God that you bear that name.’ 1 Peter 4:12-14, 16.
2) It is from God. Now, there are a few possible understandings here. Either Paul is stating that the Philippians’ salvation is from God, which is obvious, or he is asserting that the opposition, the sign of salvation, their courage – all of it – is from God. The latter appears to be better with the context and logic of Paul’s thought in the epistle, as well as the grammar of the sentence. Essentially, the Philippians can have boldness and courage in the face of opposition because they know that God has purposely not withheld it. Silva summarizes it perfectly: ‘The true grounds for the Philippians’ encouragement was the profound conviction that nothing in their experience took place outside God’s superintendence.’ There is a sense whereby the Christian views their suffering and opposition directly from God. Believing the sovereign power of God, it is easily conceded that if God did not want them to suffer or be opposed, then they would not suffer or be opposed.
 Silva notes that the difficult grammar of 1:28 indicates that the last clause refers to the whole, not merely salvation. The feminine noun soteria is not the grammatical antecedent of touto (this), which is a neuter pronoun. 83.
 Silva, 83.