Proverbs 6:23

כִּי נֵר מִצְוָה וְתוֹרָה אוֹר וְדֶרֶךְ חַיִּים תּוֹכְחוֹת מוּסָר

Because a commandment is a candle, Torah is light, and instructional corrections are the path of life.

The context, as we see from the previous verse, is the protection that one receives in the Next World from the merits that he earned in this world. The Talmud in Sotah (21a) explains that the merit of a mitzvah is like a candle – it will light one’s way but only for so long. The merit of Torah, however, is like light itself, which endures eternally.