The grave does not impede progress toward a closer union with Him. It is only this degree of closeness to Him which we consider when we celebrate All Saints one day, and All Souls the next. Purgatory is a great blessing because it shows those who love God how they failed in love, and heals their ensuing shame. Most of us have neither fulfilled the commandments nor failed to fulfill them. Our very mediocrity shames us.
Purgatory fills in the void.
We learn finally what to fulfill all of them means. Most of us neither hate nor fail completely in love. Purgatory teaches us what radical love means, when God remakes our failure to love in this world into the perfection of love in the next. As the sacraments on earth provide us with a process of transformation into Christ, so purgatory continues that process until the likeness to Him is completed. It is all grace.