How can the prophetic hadiths be reconciled that indicate "the pens have been lifted and the pages have dried," and "no caution will benefit against destiny," with the hadiths that affirm "supplication benefits against what has descended and what has not descended," and "nothing averts destiny except supplication"?

There is no contradiction between the hadiths related to du'a' (supplication) and qada' (divine decree), for Allah has linked qada' to certain causes, among which is du'a'. Calamity is a decree, and repelling it with du'a' is also a decree, as Ibn al-Qayyim mentioned that the faqih (jurist) is one who repels destiny with destiny. Some scholars, such as al-Tahawi and al-Ghazali, reconciled these hadiths, explaining that Allah may determine a person's lifespan or destiny based on their actions, such as du'a' and righteousness. Sheikh Ibn 'Uthaymeen was asked about the meaning of "Nothing repels qada' except du'a'" and he replied that du'a' is a cause among the causes of qada'. If Allah decrees an illness for someone, and then they supplicate, Allah may remove the illness from them, and that would be by His decree. As for what "the pens have dried upon," it refers to what is written in the Preserved Tablet (Al-Lawh Al-Mahfuz) and does not change. However, what changes is what is in the scriptures of the angels, where lifespan may increase or decrease according to deeds such as maintaining kinship ties.