What is the grammatical and semantic difference between the letter fa (ف) and the letter waw (و), and when is each used? What is the significance of the fa in His Almighty's saying: "Then for them is their reward with their Lord"?

The Arabic letters "fa" (ف) and "waw" (و) each have different meanings in the language. "Fa" (ف) can be a conjunction indicating sequence, immediate succession, or causality; it can also be a linking particle for an answer (jawab), or an extra (za'idah) particle. As for "waw" (و), it can be used for conjunction (indicating absolute co-occurrence without sequence), for starting a new sentence (ista'naf or ibtida'), for concomitance (ma'iyyah), as an extra (za'idah) particle, and as the "waw of eight" (waw al-thamaniyah). Grammarians may differ on these meanings.

Regarding the verses, it is probable that the "waw" in the Almighty's saying: "And when he had furnished them with their provision, he said: 'Indeed, you are thieves!'" (وَلَمَّا جَهَّزَهُم بِجَهَازِهِمْ قَالَ إِنَّكُمْ لَسَارِقُونَ) is a conjunction, meaning that after he had furnished them and settled their affairs, he said that to them, based on a previous dialogue between Joseph and his brothers. As for the "fa" in the Almighty's saying: "So when he had furnished them with their provision, he put the drinking cup in his brother’s saddlebag" (فَلَمَّا جَهَّزَهُم بِجَهَازِهِمْ جَعَلَ السِّقَايَةَ فِي رَحْلِ أَخِيهِ), it is probable that it indicates immediate succession, meaning that immediately after furnishing them, he put the drinking cup in his brother’s saddlebag.