When God made His covenant with Abraham, there was a sign of the covenant which was circumcision. Everyone would know that a man who had been circumcised was a covenant partner with God. When God made His covenant with Moses, there was a sign of the covenant; keeping the Sabbath. Everyone would know that the Israelites were God’s covenant people because they kept the Sabbath. The New Covenant established by Christ has a sign also, and that is that we are imitators of Jesus Christ, and this is what Paul is referring to here. Everyone who sees a person living as Christ would live knows they are seeing Christ’s covenant partner. This imitation of Christ has little to do with following a written code of rules and regulations, it has everything to do with loving others and putting others first. It also has to do with putting such a high priority on His love that we will be willing to endure hardship at the hands of those who oppose Christ.
The last part of this passage refers to suffering and enduring a struggle. Our struggle isn’t really with any person or persons, for those who oppose the gospel really don’t have a clue what is at stake. Our struggle is with the spiritual forces that are in opposition to Christ, just as Paul’s struggle was. Recall that Paul didn’t seem to hate his captors, far from it in fact, for He was there in jail, sharing Christ’s love with them, and this is exactly the kind of thing he is calling upon each of us to do.