John Wesley on Exodus 27:20

We read of the candlestick in the 25th chapter; here is order given for the keeping of the lamps constantly burning in it. 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, Zech 4:11,12. The priests were to light the lamps, and to tend them; to cause the lamp to burn always, night and day. Thus it is the work of ministers to preach and expound the scriptures, which are as a lamp to enlighten the church. 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.