Exodus 27:20

We read of the candlestick in the twenty-fifth chapter; here is an order given for the keeping of the lamps constantly burning in it, else it was useless; in every candlestick there should be a burning and shining light; candlesticks without candles are as wells without water or as clouds without rain. Now, 1. The people were to provide the oil; from them the Lord's ministers must have their maintenance. Or, rather, the pure oil signified the gifts and graces of the Spirit, which are communicated to all believers from Christ the good olive, of whose fulness we receive (Zac 4:11, Zac 4:12), and without which our light cannot shine before men. 2. The priests were to light the lamps, and to tend them; it was part of their daily service to cause the lamp to burn always, night and day; thus it is the work of ministers, by the preaching and expounding of the scriptures (which are as a lamp), to enlighten the church, God's tabernacle upon the earth, and to direct the spiritual priests in his service. This is to be a statute for ever, that the lamps of the word be lighted as duly as the incense of prayer and praise is offered.

— Matthew Henry's Concise Commentary (public domain)

pure oil olive beaten--that is, such as runs from the olives when bruised and without the application of fire. for the light . . . Aaron and his sons--were to take charge of lighting it in all time coming.

— Jamieson-Fausset-Brown Commentary (public domain)