15:15-21 Christ met death in its greatest terror. It was the death of the vilest malefactors. Thus the cross and the shame are put together. God having been dishonoured by the sin of man, Christ made satisfaction by submitting to the greatest disgrace human nature could be loaded with. It was a cursed death; thus it was branded by the Jewish law, De 21:23. The Roman soldiers mocked our Lord Jesus as a King; thus in the high priest's hall the servants had mocked him as a Prophet and Saviour. Shall a purple or scarlet robe be matter of pride to a Christian, which was matter of reproach and shame to Christ? He wore the crown of thorns which we deserved, that we might wear the crown of glory which he merited. We were by sin liable to everlasting shame and contempt; to deliver us, our Lord Jesus submitted to shame and contempt. He was led forth with the workers of iniquity, though he did no sin. The sufferings of the meek and holy Redeemer, are ever a source of instruction to the believer, of which, in his best hours, he cannot be weary. Did Jesus thus suffer, and shall I, a vile sinner, fret or repine? Shall I indulge anger, or utter reproaches and threats because of troubles and injuries?

Verses 17, 18. - And they clothe him with purple, and plaiting a crown of thorns, they put it on him; and they began to salute him, Hail, King of the Jews! They clothe him with purple (ἐνδύουσιν αὐτὸν πορφύραν). So also says St. John (John 21:2, ἱματιον πορφυροῦν). St. Matthew says (Matthew 27:28), "They put on him a scarlet robe (περιέθηκαν αὐτῷ χλαμύδα)." Purple and scarlet are not such very dissimilar colors. Purple is a royal color; and the chlamys of St. Matthew was a short military cloak of scarlet, intended to be a kind of royal livery. St. Cyril says that the purple cloak symbolized the kingdom of the whole world, which Christ was about to receive, and which he was to obtain by the shedding of his most precious blood. It was designed in mockery of his claim to be a King, and it probably bad a reference to his supposed insurrection against Caesar. All this was permitted by Pilate, in order that he might the more easily, after this ignominious treatment, deliver Christ from the extreme sentence. And plaiting a crown of thorns, they put it on him. The crown of thorns was in all probability woven from the Zizyphus spina Christi (the nabk of the Arabs), which grows abundantly in Palestine, fringing the banks of the Jordan. This plant would be very suitable for the purpose, having flexible branches, with leaves very much resembling the ivy leaf in their color, and with many sharp thorns. The pain arising from the pressure of these sharp thorns upon the head must have been excruciating. And they began to salute him, Hail, King of the Jews! (Ξαῖρε βασιλεῦ τῶν Ἰουδαίων). This word, χαῖρε, was an ancient form of salutation; here used by the soldiers in bitter mockery of his claim to be a king.

And they clothed him with purple,.... Matthew calls it a "scarlet" robe; and the Persic version here renders it a "red garment": it was of a colour resembling purple; it was pretty near it, and therefore so called; which is what kings were used to wear; and so in derision of him, as a king, clothed him with this mock purple robe; and which was very likely one of the soldiers' old coats:

and platted a crown of thorns, and put it about his head; for a crown, and also a reed in his hand, instead of a sceptre, as Matthew relates; See Gill on Matthew 26:28, Matthew 26:29.

15:17 Purple - As royal robes were usually purple and scarlet, St. Mark and John term this a purple robe, St. Matthew a scarlet one. The Tyrian purple is said not to have been very different from scarlet.

Mark 15:17 Parallel Commentaries
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