No doubt Joshua had ascended the heights, most likely those to the north of the valley, so as to separate himself from the flying Israelites on the lower ground, and to be visible to the men in ambush behind the city. He now, at the command of God, gives the appointed signal to the ambush.

Stretch out the spear - It is very probable that Joshua had a flag or ensign at the end of his spear, which might be easily seen at a considerable distance; and that the unfurling or waving of this was the sign agreed on between him and the ambush. (see Joshua 8:13, and the preceding observations on Joshua 8:1 (note), observation 6); and on seeing this flag or ensign unfurled, the men who lay in ambush arose and entered the city, making the fire previously agreed on. See Joshua 8:8.

And the Lord said unto Joshua, stretch out the spear that is in thy hand towards Ai,.... On which was a flag, as Abarbinel and Ben Melech think; and which is not improbable, and served for a signal for the ambush to come out and seize the city, as both they and Jarchi observe, as well as a signal also to the army of Israel to prepare to turn and face about, and engage with the enemy; though they did not actually do this until they saw the smoke of the city, Joshua 8:21,

for I will give it into thine hand; of which the stretching out of his spear seems also to be a confirming sign to him, and which he kept stretched out until all the inhabitants of Ai were destroyed, Joshua 8:26,

and Joshua stretched out the spear that he had in his hand toward the city: and therefore must turn himself towards it; and it is highly probable that at the same time there was a full stop of the army, and that they immediately turned or prepared to turn about.

At the command of God Joshua now stretched out the javelin in his hand towards the town. At this sign the ambuscade rose hastily from its concealment, rushed into the town, and set it on fire. בּכּידון נטה signifies to stretch out the hand with the spear. The object יד, which is missing (cf. Joshua 8:19, Joshua 8:26), may easily be supplied from the apposition בּידך אשׁר. The raising of the javelin would probably be visible at a considerable distance, even if it was not provided with a small flag, as both earlier and later commentators assume, since Joshua would hardly be in the mist of the flying Israelites, but would take his station as commander upon some eminence on one side. And the men in ambush would have scouts posted to watch for the signal, which had certainly been arranged beforehand, and convey the information to the others.

And the LORD said unto Joshua, {h} Stretch out the spear that is in thy hand toward Ai; for I will give it into thine hand. And Joshua stretched out the spear that he had in his hand toward the city.

(h) Or, lift up the banner to signify when they should invade the city.

8:18 Stretch out the spear - This was, either, for a sign to his host present with him, to stop their flight, and make head against the pursuers: or, for a signal to the liers in wait, or, as a token of God's presence and assistance with them, and of their victory.

18-25. Joshua stretched out the spear that he had in his hand toward the city-The uplifted spear had probably a flag, or streamer on it, to render it the more conspicuous from the height where he stood. At the sight of this understood signal the ambush nearest the city, informed by their scouts, made a sudden rush and took possession of the city, telegraphing to their brethren by raising a smoke from the walls. Upon seeing this, the main body, who had been reigning a flight, turned round at the head of the pass upon their pursuers, while the twenty-five thousand issuing from their ambuscade, fell back upon their rear. The Ai-ites surprised, looked back, and found their situation now desperate.

8:3-22 Observe Joshua's conduct and prudence. Those that would maintain their spiritual conflicts must not love their ease. Probably he went into the valley alone, to pray to God for a blessing, and he did not seek in vain. He never drew back till the work was done. Those that have stretched out their hands against their spiritual enemies, must never draw them back.