وَأَجمِلand be gracious إِذاif ماemphatic particle كُنتَyou are لاno بُدَّalternative مانِعاًwithholding
وَأَجمِل إِذا ما كُنتَ لا بُدَّ مانِعاً
وَقَدand sometimes يَمنَعُwithholds الشَيءَthe thing الفَتىthe young man وَهوَwhile he مُجمِلُgracious
وَقَد يَمنَعُ الشَيءَ الفَتى وَهوَ مُجمِلُ
Be gracious when you cannot but refuse,
And be gracious if you have no choice but to withhold;
For a man may deny a request and still be gracious.
And a young man may withhold something while remaining gracious.
Sol 6.1