ما كل بارقةٍ تجود بمائه


This is an Arabic saying, or "مَثَلٌ".


Words
بارقة
A thunder cloud.

جادَ يجودُ
This word means "He was generous" or "gave generously".

Grammar
ما
This is called in Arabic "ما الحجازية" and behaves just like "ليْس". It makes the "اسم ما" become "مرفوع" and the "خبر ما" become "منصوب".

Example
ما محمدٌ كاذباً
Muhammad is not a liar.

So the "اسم ما" in the 'Proverb' is "كًلُّ" and the "خبر ما" is the sentence, consisting of "فعل و فاعل" of "تجودُ" .

Meaning of proverb
As anyone who has lived in saudi would know, when it rains in saudi, it pours!!! A lot. with thunder, lightning, the works. Everything gets flooded, the dry valleys come alive with running water, and the once dry desert comes alive with plants that literally grow overnight.
As Allaah said in the Qur'aan

وَمِنْ آيَاتِهِ أَنَّكَ تَرَى الْأَرْضَ خَاشِعَةً فَإِذَا أَنزَلْنَا عَلَيْهَا الْمَاءَ اهْتَزَّتْ وَرَبَتْ إِنَّ الَّذِي أَحْيَاهَا لَمُحْيِي الْمَوْتَىٰ إِنَّهُ عَلَىٰ كُلِّ شَيْءٍ قَدِيرٌ

And of His signs is that you see the earth stilled, but when We send down upon it rain, it quivers and grows. Indeed, He who has given it life is the Giver of Life to the dead. Indeed, He is over all things competent.

Therefore, Thunder clouds are a usual indication of rainfall, and the decent of provision from the skies. So although there is a negative association with thunder clouds in the west, in desert lands, it is the opposite.
So the proverb makes a resemblance between a thunder cloud and a generous rich man. This is done by the use of the word "جاد" which means to give of ones wealth in charity, or in goodness. So the meaning is that maybe a thundercloud, being like a man who has wealth that we can benefit from, may not share his wealth with us.

So things that may look positive and good, may not turn out the way you expect it, just like a thunder cloud holding rain or a rich man with his pockets filled with gold coins, may not give/share it with us.