To arrest Jesus
To kill him.
But they said.
‘Not during the festival!
There may be a riot
Among the people.’”
καὶ συνεβουλεύσαντο ἵνα τὸν Ἰησοῦν δόλῳ κρατήσωσιν καὶ ἀποκτείνωσιν·
ἔλεγον δέ Μὴ ἐν τῇ ἑορτῇ, ἵνα μὴ θόρυβος γένηται ἐν τῷ λαῷ.
This is almost word for word to Mark, chapter 14:1-2, and somewhat similar to Luke, chapter 22:2. Matthew said that these elders and priests conspired or plotted (καὶ συνεβουλεύσαντο) to arrest Jesus (ἵνα τὸν Ἰησοῦν κρατήσωσιν) and kill him (καὶ ἀποκτείνωσιν·) by some secret deceitful trick (δόλῳ). However, they did not want to do it during the Passover festival (ἔλεγον δέ Μὴ ἐν τῇ ἑορτῇ). They were afraid that there might be a disturbing riot among the people (ἵνα μὴ θόρυβος γένηται ἐν τῷ λαῷ). What made them change their minds?