The sentence is kind of poetic) and it means "The sky won´t be grey forever if I have hope and faith." "Да и" is an intensifier which is used in the meaning of " and also","additionally" (to what has already been said before), and "раз" means "in case" in this context. I hope this helped)

Good examples from the Bible: И сказал Аврам Лоту: да не будет раздора между мною и тобою, и между пастухами моими и пастухами твоими, ибо мы родственники; And Abram said unto Lot, Let there be no strife, I pray thee, between me and thee, and between my herdmen and thy herdmen; for we [be] brethren. да не будет у тебя других богов пред лицем Моим Thou shalt have no other gods before me.

Да и не будет= just не будет///раз=если This is gain intonation in Russian

I believe, that the sunny days(good days) will come, because i hope in it