And when they had sung a hymn - The Passover was observed by the Jews by singing or "chanting" Ps. 113-118. These they divided into two parts. They sung Ps. 113-114 during the observance of the Passover, and the others at the close. There can be no doubt that our Saviour, and the apostles also, used the same psalms in their observance of the Passover. The word rendered "sung a hymn" is a participle, literally meaning "hymning" - not confined to a single hymn, but admitting many.
Mount of Olives - See the notes at Matthew 20:1.

And when they had sung a hymn - Υμνησαντες means, probably, no more than a kind of recitative reading or chanting. As to the hymn itself, we know, from the universal consent of Jewish antiquity, that it was composed of Psalm 113:1-9, Psalm 114:1-8, 115, 116, Psalm 117:1-2, and 118, termed by the Jews הלל halel, from הללו־יה halelu-yah, the first word in Psalm 113:1-9. These six Psalm were always sung at every paschal solemnity. They sung this great hillel on account of the five great benefits referred to in it; viz.
1. The Exodus from Egypt, Psalm 114:1. When Israel went out of Egypt, etc.
2. The miraculous division of the Red Sea, Psalm 114:3. The sea saw it and fled.
3. The promulgation of the law, Psalm 114:4. The mountains skipped like lambs.
4. The resurrection of the dead, Psalm 116:9. I will walk before the Lord in the land of the living.
5. The passion of the Messiah, Psalm 115:1. Not unto us, O Lord, not unto us, etc.
See Schoettgen, Hor. Hebr. p. 231, and my Discourse on the nature and design of the Eucharist, 8vo. Lond. 1808.

And when they had sung (q) an hymn, they went out into the mount of Olives.
(q) When they had made an end of their solemn singing, which some think was six Psalm, (Psalm 112:1; Psalm 117:2).

And when they had sung an hymn,.... The "Hallell", which the Jews were obliged to sing on the night of the passover; for the passover, they say (l), was , "bound to an hymn". This "Hallell", or song of praise, consisted of six Psalm, the 113th, 114th, 115th, 116th, 117th, and 118th (m): now this they did not sing all at once, but in parts. Just before the drinking of the second cup and eating of the lamb, they sung the first part of it, which contained the 113th and 114th Psalm; and on mixing the fourth and last cup, they completed the "Hallell", by singing the rest of the Psalm, beginning with the 115th Psalm, and ending with the 118th; and said over it, what they call the "blessing of the song", which was Psalm 145:10, &c., and they might, if they would, mix a fifth cup, but that they were not obliged to, and say over it the "great Hallell", or "hymn", which was the 136th Psalm (n). Now the last part of the "Hallell", Christ deferred to the close of his supper; there being many things in it pertinent to him, and proper on this occasion, particularly Psalm 115:1, and the Jews themselves say (o), that , "the sorrows of the Messiah" are contained in this part: that this is the hymn which Christ and his disciples sung, may be rather thought, than that it was one of his own composing; since not only he, but all the disciples sung it, and therefore must be what they were acquainted with; and since Christ in most things conformed to the rites and usages of the Jewish nation; and he did not rise up from table and go away, until this concluding circumstance was over; though it was allowed to finish the "Hallell", or hymn, in any place they pleased, even though it was not the place where the feast was kept (p) however, as soon as it was over,
they went out to the Mount of Olives; he and his disciples, excepting Judas: first he himself alone, and then the disciples followed him, according to Luke 22:39, and the Persic version here reads it, "he went out". This seems to be contrary to a Jewish canon; for the passover was , "bound to lodging a night" (q); that is, as the gloss explains it,
"the first night (i.e. of the passover) a man must lodge in Jerusalem; thenceforward it was lawful to dwell without the wall, within the border.
And a little after, the same phrase, being bound to lodge, is explained, one night in the midst of the city: but Christ had more important business to attend unto, than to comply with this rule, which was not obligatory by the word of God, though the Jews pretend to found it on Deuteronomy 16:7 (r). The place where he went with his disciples, was the Mount of Olives, which was on the east side of Jerusalem; and was the place where the high priest stood, and burnt the red heifer, and sprinkled its blood (s): now from the temple, or from the mountain of the house, there was a causeway, or bridge on arches, made to the Mount of Olives, in which the high priest and the heifer, , "and all his assistants", (the priests that helped him in this service,) went to this mount (t): in this same way it is very probable, went Christ the great high priest, who was typified by the red heifer, and his companions the disciples, to the same place, where he had his bloody sweat, and where his sorrows and sufferings began,
(l) Misn. Pesach. c. 9. 3. T. Bab. Pesach. fol. 95. 1, 2. (m) Seder Tephillot, fol. 101, &c. Ed. Amstelod. (n) Maimon. Hilch. Chametz Umetzah, c. 8. sect. 5. 10. (o) T. Bab. Pesachim, fol. 118. 1. (p) Maimon. ut supra. (Hilch. Chametz Umetzah, c. 8. sect. 5. 10.) (q) T. Bab. Pesach. fol. 95. 2. (r) Talmud ib. & Jarchi in Dent. xvi. 7. (s) Misn. Middot, c. 2. sect. 4. T. Bab. Yoma, fol. 16. 1. (t) Misn. Parah, c. 3. sect. 6. & Middot, c 1. sect. 3. & Maimon. & Bartenora in ib.

When they had sung a hymn. It was customary to conclude the passover by singing the Psalm from 115th to 118th.
To the mount of Olives. To the garden of Gethsemane, which was on the slope of the mount. This journey over the Kedron to Gethsemane was made in the darkness of the night. The Lord's Supper, a memorial of his death, has a still more tender interest, from the fact that it was established only two or three hours before he was betrayed and seized.

And when they had sung the hymn - Which was constantly sung at the close of the passover. It consisteth of six psalms, from the 113th to the 118th. Psalm 113:1 &c. The mount of Olives - Was over against the temple, about two miles from Jerusalem. Mark 14:26; Luke 22:39; John 18:1.