To what extent is it true that avoiding major sins makes the five daily prayers and other acts of worship effective in expiating sins, and that the five daily prayers do not have an effect in expiating sins unless major sins are avoided, and that the verse "If you avoid the major sins which you are forbidden from, We will remove from you your lesser sins" means the expiation of lesser sins through expiators like the five daily prayers?

This is a lengthy issue that has been discussed by many scholars, including Ibn Hazm, Ibn Abd al-Barr, and Ibn Atiyyah. Among those who best compiled its scattered parts and hadiths is Ibn Rajab in his book (Jami’ al-Ulum wal-Hikam) when explaining the hadith: "Fear Allah wherever you are, and follow up a bad deed with a good deed, it will erase it." One may also refer to the tafsir of Ibn Kathir and Al-Shawkani when interpreting the Almighty's saying: "If you avoid the major sins which you are forbidden from" {An-Nisa: 31}.