The letter of Paul to the Philippian church has been accurately called the epistle of joy. While Paul was in a Roman prison cell, the delivered messages from his friends at Philippi were sources of great joy as he remembered their faith and dedication to God. He wrote this letter of Philippians to those same folks, to let them know the happiness and joy he experienced when he learned of their work and the testimony of their lives.
In the third chapter of Philippians, Paul gives a discourse on what it means to really belong to Jesus, even citing some of his own personal history, which he thought at the time to be truthful and an accurate assessment of the things God was expecting of him. He called himself a Hebrew of Hebrews; in regard to the law, a Pharisee; as for zeal, Paul was always zealous for persecuting Christians and the church; and as for knowing and living the absolute truth, he claimed to be faultless.
Now Paul is saying that all of those accomplishments are nothing but rubbish, because the real substance of attaining righteousness is not of himself, but only through Jesus. Many changes had been made in Paul's life since his encounter with the resurrected Jesus on the road to Damascus. He now knows that the sense of righteousness based on his own accomplishments isn't righteousness at all. Only that which comes from God through faith in Christ is the righteousness that saves. That is what led Paul to proclaim in Philippians 3: 10-11, "I want to know Christ and the power of his resurrection and the fellowship of sharing in his sufferings, becoming like him in his death, and so, somehow, to attain to the resurrection from the dead."
Paul readily admitted that he had not yet achieved those things, nor did he consider himself perfect. He confesses that he is striving to press on and take hold of that for which Christ Jesus had taken hold of him. Then notice verses 13 and 14, "Brothers, I do not consider myself yet to have taken hold of it. But one thing I do: Forgetting what is behind and straining toward what is ahead, I press on toward the goal to win the prize for which God has called me heavenward in Christ Jesus."
There is some good advice for the Philippians in Paul's statement following those words, "But one thing I do:" Read them yourself because it's pretty good advice for you and me, too.
Forgetting what is behind..... That means if you have accomplished great things, forget them. Your accomplishments cannot save you. If you have been successful in business, or education, or parenting, or generosity, or even ministry, those things are in the past! Forget what is behind you. Remember, we are pressing on.
Straining toward what is ahead.... What is ahead for us? It's really a dedication to making the right decision to press on toward the goal; to win the prize in which God calls us toward heaven. Paul was saying this, not only for his benefit, but also for all Christians of all generations. Our main objective is to love and honor and praise God, because he is calling us heavenward. All else is futile, all else is rubbish.