Or HaChaim on Leviticus 10:2/אור החיים על ויקרא י׳:ב׳

1 וימותו לפני השם. They died in the presence of the Lord. The words: "in the presence of the Lord" may be intended to inspire fear and reverence for the Tabernacle in the people who witnessed that even people who entered in order to offer the offering dearest to G'd, incense, had died as a result of doing something unauthorised. There is also an allusion here that their death was due to something they had done previously and which involved the presence of G'd. I refer to Exodus 24,10 where these two sons were reported as having beheld G'd (compare Vayikra Rabbah 20,10 and G'd was reported there as not punishing the "nobles of Israel" at that time). These "nobles" were Nadav and Avihu.