لِنَجْلِبَ الرَّشْحَ إِلَى الْحَظِّ الصَّدِي
So that we may bring a little moisture to our parched fortune.
Rashḥ is a small trickle or seepage, while ṣadī means parched with thirst. Fortune is personified as thirsty, and a small gift becomes the moisture it needs. This magnifies how valuable even modest assistance seems to the speakers.