‘And the word of Yahweh came to me saying, “Son of man, set your face towards the children of Ammon and prophesy against them, and say to the children of Ammon, “Thus says the Lord Yahweh, because you said “Aha” against my sanctuary when it was profaned, and against the land of Israel when it was made desolate, and against the house of Judah when they went into captivity.” '
The opening phrase ‘the word of Yahweh came to me saying' (compare Ezekiel 26:1; Ezekiel 27:1; Ezekiel 28:1; Ezekiel 28:11; Ezekiel 28:20; Ezekiel 29:1; Ezekiel 29:17; Ezekiel 30:1; Ezekiel 30:20; Ezekiel 31:1; Ezekiel 32:1; Ezekiel 32:17) indicates the commencement of a new oracle. Thus the oracles against Ammon, Moab, Edom and Philistia are as one oracle.
‘Son of man.' This method of address to Ezekiel continues throughout the book. It is a reminder to him that he is but an earthly man being approached by the God of creation. It is a reminder of his weakness and creatureliness, a warning against presumption. But it also contains within it in its frequency a sense of having been chosen. He is that ‘son of man' whom God has chosen out as His instrument and mouthpiece and addresses personally. Thus it inculcates humility and loving confidence and response.
‘Set your face.' While this may be seen only as a general instruction, it may be that Ezekiel did actually ‘set his face' in that direction to indicate more directly the power of the word of Yahweh going forth.
Ezekiel 25:3 now introduces the ‘because --', the charge laid against Ammon. At first sight in context this may well be seen as referring to a time after the destruction of Jerusalem when Ammon shook their heads knowingly because Yahweh had been unable to protect His people and Jerusalem, and the temple lay in ashes and the land lay desolate.
But it could equally apply to the period when Jerusalem was under siege, and the Egyptians who came to offer aid had withdrawn, with the ‘wise' Ammonites realising that Jerusalem's situation was hopeless and that Yahweh could no longer help them, and standing aside, and doing nothing but say ‘Aha'.
The descriptions fit both situations. Ezekiel had spoken of the sanctuary as having already been profaned before the final destruction (Ezekiel 23:39), along with Yahweh's holy things (Ezekiel 22:26), partly because the Jerusalemites had offered their children through fire to Molech the god of these very Ammonites. This may well have made the children of Ammon say ‘Aha' as they saw their god triumphing in Jerusalem.
And the land of Israel had been made desolate long before, at which point Ammon had taken advantage of the situation and had been condemned for it (Jeremiah 49:1-6), and it had been made desolate again by Nebuchadnezzar's approach to Jerusalem. Furthermore the ‘house of Judah' could be seen as having been taken into captivity twice in previous invasions (2 Kings 24:13-15; 2 Chronicles 36:5-6 with Daniel 1:1-4), both times when Ammon might well have said ‘Aha' as they themselves took part, (certainly the first time), in the war on Babylon's side (2 Kings 24:2).
Note in this regard that Ezekiel has up to this point only rarely used the phrase ‘the house of Judah', and then to specifically distinguish it from Israel in the north (Ezekiel 4:6), and usually speaks of ‘the house of Israel' to include both, seeing both the Jerusalemites and the exiles and all Israel as the house of Israel. Thus the use here may suggest that the previous captivities are in mind. The final captivity would, in Ezekiel's mind, be ‘of Israel'.
So there are good reasons why this oracle may have been given while Jerusalem was surrounded and before its final downfall.
Either way the point is that God has seen their attitude towards His people and will punish them for it.