The first question on Judgement Day
أَوَّلُ مَا يُحَاسَبُ بِهِ الْعَبْدُ يَوْمَ الْقِيَامَةِ مِنْ عَمَلِهِ الصَّلَاةُ، فَإِنْ صَلُحَتْ صَلُحَ سَائِرُ عَمَلِهِ
Awwalu ma yuhasabu bihi-l-'abdu yawma-l-qiyamati min 'amalihi-s-salah, fa-in saluhat saluha sa'iru 'amalih.
"The first thing the servant will be asked about on the Day of Resurrection, from his deeds, is the prayer. If it is sound, the rest of his deeds will be sound."
Narrated by Abu Hurayrah. Jami' at-Tirmidhi 413 (sahih)
A short reflection
Everything else gets graded after salah. It's the load-bearing wall of the whole building.