The simple explanation of “when they drew near before God and died” (Lev. 16:1) is that God strikes these people and, as a result, those who are near recoil, and He is thus sanctified.
Sometimes, however, those who draw near suffer an even worse type of death: an internal death.
The Talmud says of Aaron’s sons: “Only their souls were burned, but their bodies remained intact” (Sanhedrin 52a).
This kind of death can befall any of us today as well – one continues to fulfill mitzvot, to sway during prayer, but his soul has burned up and left him.
“When they drew near before God,” their souls were burned, “and they died.”
–Rabbi Adin Steinsaltz