That the soldiers spat upon him signified contempt or hatred; for biblical examples see Numbers 12.14; Deuteronomy 25.9; Job 30.10; Isaiah 50.6. See also 26.67 and comments.

When the soldiers took the reed and struck him on the head they intended not only to hurt him physically, but to insult him. At least this is the significance that the action would have in a Jewish context (see 5.39).

Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .