And Joshua made peace with them, and made a covenant with them, to let them live: and the leaders of the congregation swore to them.
Read Chapter 9
Ambrose of Milan
Then the Gibeonites, fearing his strong hand, came with guile, pretending that they were from a land very far away, and by traveling so long had rent their shoes and worn out their clothing, of which they showed proofs that it was growing old. They said, too, that their reason for undergoing so much labor was their desire to obtain peace and to form friendship with the Hebrews, and [they] began to ask Joshua to form an alliance with them. And he, being as yet ignorant of localities and not knowing anything of the inhabitants, did not see through their deceit, nor did he enquire of God but readily believed them.
So sacred was one’s promised word held in those days that no one would believe that others could try to deceive. Who could find fault with the saints in this, namely, that they should consider others to have the same feelings as themselves and suppose no one would lie because truth was their own companion? They do not know what deceit is, they gladly believe of others what they themselves are, while they cannot suspect others to be what they themselves are not. Hence Solomon says, “An innocent man believes every word.” We must not blame his readiness to believe but should rather praise his goodness. To know nothing of anything that may injure another, this is to be innocent. And although he is cheated by another, still he thinks well of all, for he thinks there is good faith in all. - "Duties of the Clergy 3.10.67–68"