What is the ruling on sincere repentance from abandoning prayer out of laziness, and does it nullify what preceded it? And how can one make up many missed prayers?

Praise be to Allah, who has accepted your repentance from abandoning prayer. Sincere repentance erases what came before it. Scholars have differed on the obligation of making up intentionally missed prayers. The majority holds that making them up is obligatory, while others believe that supererogatory prayers and repentance suffice. The more cautious approach is to make them up. A Muslim may follow the opinion of someone whose knowledge he trusts. As for how to make them up, Maliki jurists may allow making up two days' prayers with each day, but the more cautious approach is to make them up according to one's capacity without causing harm.