Several adjectives precede the command contained in this text. Not only does Paul twice use "dearly beloved" to describe his relationship with the Philippians, but he also insists that he longs for them and anticipates joy at the recognition of the "crown" he will receive in heaven.
These are intense words. Agapetos is the descriptive Greek term translated "dearly beloved." The Heavenly Father uses agapetos to express His love for His "beloved Son" (Matthew 3:17). Most of the New Testament letters freely use agapetos to describe various personal relationships with their brothers and sisters in Christ. That unique and deeply spiritual love is what demonstrates our difference to the unsaved (John 13:34-35).
Since Paul is separated from the Philippian church (probably writing the letter from Rome), his love for them caused him to "long after [them] all in the bowels of Jesus Christ" (Philippians 1:8). That passionate ache is mitigated by the joy coming from the certain knowledge that his work will result in a "victor's crown" (Greek stephanos, today's verse) when God rewards our service. "For what is our hope, or joy, or crown of rejoicing? Are not even ye in the presence of our Lord Jesus Christ at his coming?" (1 Thessalonians 2:19).
So, "stand fast in one spirit, with one mind striving together for the faith of the gospel" (Philippians 1:27). "Watch ye, stand fast in the faith, quit you like men, be strong" (1 Corinthians 16:13). Stand fast in the liberty that salvation provides. Don't become tangled up in the bondage of legalistic burdens (Galatians 5:1). "For now we live, if ye stand fast in the Lord" (1 Thessalonians 3:8). HMM III