وَلَقَدْ عَهِدْنَا إِلَى آدَمَ مِن قَبْلُ فَنَسِيَ وَلَمْ نَجِدْ لَهُ عَزْمًا
“Verily We had covenanted with Adam before, but he forgot; and We did not find in him a firm resolve”
Imam Sadiq (as) explained the above verse by saying: (This verse means), Verily We had covenanted with Adam before with some words about Mohammed, Ali, Hasan, Husain, and the Imams from their progeny, but he forgot; and We did not find in him a firm resolve.” I swear to Allah that this is how this verse was revealed to Mohammed (sawa) (Al Kafi volume 1 page 416)
Regarding this verse, Imam Baqir (as) said, this verse means that (Allah) took a covenant from Adam about Mohammed (sawa) and the Imams after him but Adam neglected the covenant. Adam did not have the “firm resolve” to recognize the true status of Mohammed (sawa) and the Imams (as)
The reason behind giving the title of Ulul Azm (the owners of the “firm resolve”) to the five Ulul Azm messengers (Hazrat Nuh, Hazrat Ibrahim, Hazrat Musa, Hazrat Isa and Holy Prophet (sawa)) is that Allah took a covenant from them about Mohammed, his successors, and Mahdi (as) and his traditions. They (the five Ulul Azm messengers) testified to this covenant, and with “a firm resolve” they accepted the covenant as the truth. (Al Kafi volume 1 page 416; Taweel Al Ayat Al Zahirah page 313)
Imam Baqir (as) said, Allah took the covenant from the prophets and said, “Am I not your Lord?” The prophets replied, “Yes. You are.” Allah asked, Is Mohammed not My Messenger? Is Ali not the Commander of the Believers? Are his successors not the authorities appointed by Me? And are they not the keepers of My knowledge? Is Mahdi not the one with whom I will support My religion? Is he not the one through whom I will spread My government? Is he not the one through whom I will avenge My enemies? And is he not the one through whom the people will worship Me, willingly or unwillingly?
The prophets replied, “We believe in this covenant and we testify to this, O our Lord.”
Imam Baqir (as) continued, Adam did not deny this covenant but he did not testify to it. Therefore, the religion was announced through the five messengers who testified in Mahdi (as). However, Adam did not have the”firm resolve” to testify.
This is the meaning of the verse, “Verily We had covenanted with Adam before, but he forgot; and We did not find in him a firm resolve” (Chapter 20 verse 115). (Tafseer Al Burhan volume 5 page 191; Taweel Al Ayat Al Zahirah page 313)