"For it has been granted to you that for the sake of Christ you should not only believe in him but also suffer for his sake,"
Paul says what many Christians today don't want you to hear because Paul is not ashamed of the gospel. I mean the entire gospel, not just the good parts you tell your non-christian friends in hopes you might trick them into "faith". What good is it to "save" someone through deception lest they come to believe the entire gospel is a lie once they realize the truth.
What does Paul say? That not only is salvation a gift, but so are the sufferings we endure for his name. A gift. Because God likes to see his children suffer? Far from it! Those who suffer together strive together with one spirit and one mind for the faith of the gospel (v27). We suffer with Christ because we are in Christ and no servant is greater than his master (John 15:20). Our suffering together brings us into greater unity.
We are one Body and Christ is our head (Eph 4:15-16) because we are united in hardship. So we rejoice in our suffering (Rom 5:3-5) because through them we know we are in Christ when we suffer for his sake and the sake of the gospel (Rom 8:17). It is when we stand firm together despite suffering that is a sign to us of our salvation despite it appearing to the world that we are being destroyed (v28).
After all, those who lose their lives for Christ will save them (Mark 8:35), the one who is not ashamed of Christ, Christ will not be ashamed of him (Mark 8:38), and all who have left mother and brothers will not fail to receive a hundred fold what they have left, and with them persecutions (Mark 10:30). Don't be afraid to tell people the truth of the gospel, all of it, for half a gospel produces half a Christian with half of a salvation.