Why aren't the leaders of Umuofia suspicious when the District Commissioner invites them to the Courthouse?
The other reason the leaders of Umuofia were not suspicious was because they had been lulled into complacence by the lack of repercussions for the burning of Mr. Smith's church and Enoch's compound. Two days had been allowed to pass with no substantial response to the egwugwu's furious onslaught; even though every man in Umuofia had walked about with a gun or a machete, no response appeared to be forthcoming from the Christian quarter.
To go back to Chapter 22, the text tells us that, when Enoch performed the sacrilegious action of unmasking an egwugwu, a furor had erupted within the community of Umuofia. The Christians, fearful for their lives, had cowered in Mr. Smith's parsonage and had prayed for deliverance. Accordingly, the egwugwu had burned Enoch's compound and then had proceeded to burn Mr. Smith's church; yet, their furious actions were met with no resistance whatsoever from the Christians.
In Umuofia culture, any insult or substantial grievance was usually met with almost immediate retaliation. A case in point was the response to the murder of an Umuofian woman at the beginning of the novel. Mbaino, the offending clan, had been offered either war or the choice to pay some sort of compensation for the woman's death. The point is: Umuofia would never have neglected to react in such a situation; a lack of any sort of response would have been interpreted as cowardice on the part of the aggrieved party.
So, when the Christians did not retaliate and instead, waited for the District Commissioner to return from his trip, the general consensus was that the leaders of Umuofia had nothing to fear. Also, since the leaders of Umuofia and the Commissioner were leaders in their respective cultures, the men of Umuofia never doubted that they would be treated with understanding by the Commissioner for the wrongs they had suffered.
Unfortunately for them, the Commissioner didn't see matters in the same light. He tricked the leaders of Umuofia into complacence by his assurance that he was a reasonable man; after all, his previous actions had never led the men of Umuofia to doubt his fairness. So, the leaders of Umuofia expected to be treated like peers but instead, were handcuffed and imprisoned like common criminals. They were mistreated and abused while in captivity and only released after a fine of two hundred and fifty cowries was paid to "appease the white man." This unjust treatment led to the men of Umuofia discussing war in Chapter 24.
In Chapter 23 of Things Fall Apart, the District Commissioner invites the leaders of Umuofia to the courthouse after the church has been destroyed in his absence. The text reads,"Three days later the District Commissioner sent his sweet-tongued messenger to the leaders of Umuofia asking them to meet him in his headquarters. That also was not strange. He often asked them to hold such palavers, as he called them" (page numbers vary by edition). Part of the reason the leaders are not suspicious is because the District Commissioner has summoned them several times for "palavers," or talks, before. In addition, the messenger the District Commissioner sends is "sweet-tongued," and he speaks to them kindly.
Also, the leaders of Umuofia are used to solving their disputes in traditional ways and do not understand the Western laws by which the District Commissioner operates. For example, earlier in the novel, when a girl in Umuofia is killed by a nearby village, the other village sends Ikemefuna, a boy, to live in Umuofia with Okonkwo. When the oracle tells Okonkwo to kill the boy, he does so, even though he is very fond of him. The ways of Umuofia are different than Western ways, and the village leaders at first do not understand the power that the District Commissioner has over them. He later jails them until the villagers pay a fine. The leaders of the village are at first lured into thinking the District Commissioner poses no threat to them because he does not use guns or appear violent in a way they recognize. It is only after they are jailed that they understand his power.
It may be that you are confusing the idea of suspicion with the concept of acquiescence. The leaders of Umuofia are intelligent, alert and perceptive. They know precisely what is going on around them. Their traditions, which they rely upon for both understanding and action, cause them to be contemplative before being explosively active. This is confirmed because after Okika gives his speech to stir the leaders to rebellious action, they all remain calm while only Okonkwo springs to action, following the admonitions in Okika's speech, and attacking the whites. He finds that the leaders do not support his action, which infers that they acquiesced and rejected Okika's speech.