According to the custom of the priest's office, his lot was to burn incense when he went into the {n} temple of the Lord.

(n) The temple was one, and the court another, for Zacharias went out of the court (or outward room) where all the people were (and therefore they are said to be without) and into the temple.

People's New Testament

1:9 His lot. In the service of the sanctuary nothing was left to accident or to human arrangement. The lot determined who was to perform each separate portion of the sacred service, and especially who was each morning and evening to burn incense before the Lord.

To burn incense. Burned on the altar of incense in the Holy Place morning and evening. To burn the incense was an office held so honorable that no one was allowed to perform it twice, since it brought the offering priest nearer the divine presence in the Holy of Holies than any other priestly act, and carried with it the richest blessing from on high, which all ought to have a chance of thus obtaining.

Jamieson-Fausset-Brown Bible Commentary

9. his lot was to burn incense-The part assigned to each priest in his week of service was decided by lot. Three were employed at the offering of incense-to remove the ashes of the former service; to bring in and place on the golden altar the pan filled with hot burning coals taken from the altar of burnt offering; and to sprinkle the incense on the hot coals; and, while the smoke of it ascended, to make intercession for the people. This was the most distinguished part of the service (Re 8:3), and this was what fell to the lot of Zacharias at this time [Lightfoot].

Matthew Henry's Concise Commentary

1:5-25 The father and mother of John the Baptist were sinners as all are, and were justified and saved in the same way as others; but they were eminent for piety and integrity. They had no children, and it could not be expected that Elisabeth should have any in her old age. While Zacharias was burning incense in the temple, the whole multitude of the people were praying without. All the prayers we offer up to God, are acceptable and successful only by Christ's intercession in the temple of God above. We cannot expect an interest therein if we do not pray, and pray with our spirits, and are not earnest in prayer. Nor can we expect that the best of our prayers should gain acceptance, and bring an answer of peace, but through the mediation of Christ, who ever lives, making intercession. The prayers Zacharias often made, received an answer of peace. Prayers of faith are filed in heaven, and are not forgotten. Prayers made when we were young and entering into the world, may be answered when we are old and going out of the world. Mercies are doubly sweet that are given in answer to prayer. Zacharias shall have a son in his old age, who shall be instrumental in the conversion of many souls to God, and preparing them to receive the gospel of Christ. He shall go before Him with courage, zeal, holiness, and a mind dead to earthly interests and pleasures. The disobedient and rebellious would be brought back to the wisdom of their righteous forefathers, or rather, brought to attend to the wisdom of that Just One who was coming among them. Zacharias heard all that the angel said; but his unbelief spake. In striking him dumb, God dealt justly with him, because he had objected against God's word. We may admire the patience of God towards us. God dealt kindly with him, for thus he prevented his speaking any more distrustful, unbelieving words. Thus also God confirmed his faith. If by the rebukes we are under for our sin, we are brought to give the more credit to the word of God, we have no reason to complain. Even real believers are apt to dishonour God by unbelief; and their mouths are stopped in silence and confusion, when otherwise they would have been praising God with joy and gratitude. In God's gracious dealings with us we ought to observe his gracious regards to us. He has looked on us with compassion and favour, and therefore has thus dealt with us.