Verse 8. - At even. Literally, "between the two evenings." (See the comment on Exodus 12:6.) The offering of incense by the high priest twice a day, at the time of the morning and evening sacrifice, indicated that prayer was needed as constantly as expiation, and that neither might for a single day be intermitted. A perpetual incense. "Perpetual," in the sense that it was to be burnt twice a day, as long as the religion lasted - not in the sense that it was to be kept burning constantly.

30:1-10 The altar of incense represented the Son of God in his human nature, and the incense burned thereon typified his pleading for his people. The continual intercession of Christ was represented by the daily burning of incense thereon, morning and evening. Once every year the blood of the atonement was to be applied to it, denoting that the intercession of Christ has all its virtue from his sufferings on earth, and that we need no other sacrifice or intercessor but Christ alone.And when Aaron lighteth the lamps at even, he shall burn incense upon it,.... In the evening the priest went into the holy place to light the lamps that were gone out; see Gill on Exodus 27:20 at the same time he burnt incense on the altar; and as the daily sacrifice was offered up morning and evening, so the incense was burnt every morning and evening, and much about the same time: the Jews say (t), that the incense of the morning was offered between the blood (i.e. the sprinkling of the blood of the daily sacrifice) and the members, or the laying of the pieces on the altar; and the incense of the evening was between the pieces and the drink offering: and with this Philo agrees (u), who says, twice every day most fragrant odours were offered, at the sun rising and setting, before the morning and after the evening sacrifice:

a perpetual incense before the Lord throughout your generations; thus Christ's mediation and intercession is constant and continual; as his sacrifice continually takes away the sin of the world, in which it was the antitype of the daily sacrifice; so his blood continually speaks for peace and pardon, and every blessing of grace for his people, in which it is the antitype of the morning and evening incense; for he ever lives to make intercession; and so the prayers of the saints are directed to God both morning and evening, and they cease not praying as long as they live.

(t) Misn. Yoma, c. 3. sect. 4. (u) De Victimis, p. 836.