“Do everything without grumbling or arguing, so that you may become blameless and pure, “children of God without fault in a warped and crooked generation.” Then you will shine among them like stars in the sky as you hold firmly to the word of life. And then I will be able to boast on the day of Christ that I did not run or labor in vain.” - Philippians 2:14-16
Probably written during Paul's second incarceration in Rome. The epistle of Paul and Timothy to the Philippians suggests Paul's impending death. Paul is putting his house in order. And such stoicism may well explain Paul's verse here. Paul is not grumbling or arguing. Paul is pointing to God, to salvation. There are the facts of circumstance for which one laments. But then there is the truth of salvation for which we praise God.
In Psalm 21, David rejoices in the truth of his salvation. In Psalm 22, David Laments in the circumstance of his oppression. But we live with both truth and circumstance. And our hope is in Truth. God is our rock. He will hold us in his victory over our oppressors.
It is ok to Lament. But not to grumble. In lamentation, we list our woes to God. I lost my sister when I was eleven years old. She had been sickly all her thirteen years. And it seemed as if nothing would ever be right again. But my sister’s life was a blessing, and my life has been enriched for it. In grumbling, we diminish the blessing.