وَلَا تَقُولُوا لِمَنْ يُقْتَلُ فِي سَبِيلِ اللَّهِ أَمْوَاتٌ بَلْ أَحْيَاءٌ وَلَكِنْ لَا تَشْعُرُونَ
Do not call those killed in Allah’s path dead. Rather, they are alive, but you do not perceive it. (Al-Baqarah 2:154)
Rather, they are alive establishes the life of martyrs, while you do not perceive it shows that this life need not be accessible to ordinary senses. Life in barzakh differs from outward worldly experience.