Answered by Shaykh Faraz Rabbani
Sorry for ignorance in Questions but if repentance to Allah Most High lifts sins of past, then why do we say to make up prayers missed in past?
Answer:
In the Name of Allah, the Beneficent, the Merciful, and all blessings and peace upon our master Muhammad, his Folk, Companions and those who follow their noble way, While many actions (including repentance itself!) wipe away past sins, they do not clear past debts, whether owed to people or to Allah Most High.
The position of the overwhelming majority of the scholars of Islam, including all four schools of sunni jurisprudence is that it is obligatory to make up every single prayer missed in the past since one reached puberty or became Muslim.
Wassalam,
Faraz Rabbani.