rejoicing 'in the Lord'

"'Rejoice... and again I say, rejoice', he [Paul] reiterated in Philippians 4:4. But here and in Philippians 3:1 we note that the kind of rejoicing is qualified. It is the rejoicing 'in the Lord'. This phrase makes a difference. This is a rejoicing unrelated to worldly affairs; one that is at the foundation of being; one that has depth and height; one that stands back from the frittering worries and incidents of life. It was the kind of rejoicing that martyrs experienced in their suffering for their faith: a steady, exalted spirit that drew upon divine comfort, power and hope."