Does God forgive all major sins committed by people before completely submitting to Him?

Verses 53-54 of Chapter 39:

Say, "O My servants, who have wronged their own souls: Do not despair of Allah's mercy: surely Allah forgives all sins: He is the All-Forgiving, the All Merciful. Return to your Lord and submit to Him before the scourge overtakes you, and then you may get no help from anywhere.