See this explained in the Matthew 22:15-33 notes, and Mark 12:13-27 notes.

They watched him - Παρατηρησαντες, Insidiously watching. See on Luke 14:1 (note).

Spies - Εγκαθετους, from εν, in, and καθιημι, I let down, to set in ambush. One who crouches in some secret place to spy, listen, catch, or hurt. Hesychius explains the word by ενεδρευοντες, those who lie in wait, or in ambush, to surprise and slay. Josephus uses the word to signify a person bribed for a particular purpose. See War, b. ii. c. ii. s. 5, and b. vi. c. v. s. 2. No doubt the persons mentioned in the text were men of the basest principles, and were hired by the malicious Pharisees to do what they attempted in vain to perform.

And they watched him,.... What he said, and what he did, and where he went, that they might take an advantage against him, or know where he was, to send to him, as they should think fit, and take the best opportunity of so doing. The Syriac and Persic versions leave out this clause:

and sent forth spies which should feign themselves just men: of virtue and religion, conscientious men, that would do nothing but what was just and right, and were desirous of being exactly informed of the truth of things, that they might act right in every punctilio:

that might take hold of his words; improve them, and form a charge upon them, of sedition and treason:

that so they might deliver him unto the power and authority of the governor; the Roman governor, and by him be put to death. These men were some of them the disciples of the Pharisees, and others were Herodians; see Matthew 22:16.

Watched

See on Mark 3:2.

Spies (ἐγκαθέτους)

Only here in New Testament. From ἐγκαθίμηι, to send in, as a garrison into a city. Hence of persons sent in for the purpose of espionage.

Which should feign (ὑποκρινομένους)

Lit., feigning. Rev., which feigned. Only here in New Testament. See on hypocrites, Matthew 23:13.

The power and authority (τῇ ἀρχῇ καὶ τῇ ἐξουσίᾳ)

The former, the Roman power in general; the latter, the specific authority of the official.

{3} And they {a} watched him, and sent forth {b} spies, which should feign themselves just men, {c} that they might take hold of his words, that so they might deliver him unto the power and {d} authority of the governor.

(3) The last refuge the false prophets have to destroy the true prophets is to charge them with rebellion and treason against the state.

(a) An appropriate time to take him in.

(b) Whom they had hired deceitfully.

(c) That they might latch on to something he said, and by this forge some false accusation against him.

(d) Put him to death.

20:20-26 That they might take hold of his words. For notes on the question of the tribute money, see Mt 22:15-22. Compare Mr 12:13-17.

20:20 Just men - Men of a tender conscience. To take hold of his discourse - If he answered as they hoped he would. Mt 22:16; Mr 12:12.

Lu 20:20-40. Entangling Questions about Tribute and the Resurrection-The Replies.

20-26. sent forth-after consulting (Mt 22:15) on the best plan.

spies-"of the Pharisees and Herodians" (Mr 12:13). See Mr 3:6.

20:20-26 Those who are most crafty in their designs against Christ and his gospel, cannot hide them. He did not give a direct answer, but reproved them for offering to impose upon him; and they could not fasten upon any thing wherewith to stir up either the governor or the people against him. The wisdom which is from above, will direct all who teach the way of God truly, to avoid the snares laid for them by wicked men; and will teach our duty to God, to our rulers, and to all men, so clearly, that opposers will have no evil to say of us.