‘ And said to him, “Thus says Jephthah, Israel did not take away the land of Moab, nor the land of the children of Ammon. But when they came from Egypt, and Israel walked through the wilderness to the Sea of Reeds (to Ezion Geber - Numbers 33:35), and came to Kadesh, then Israel sent messages to the king of Edom, saying ‘Let me I pray you pass through your land. But the king of Edom did not respond. And in the same way he sent to the king of Moab, but he would not, and Israel abode in Kadesh.”
Note the majestic opening, ‘thus says Jephthah'. Jephthah wanted the king of Ammon to recognise with whom he was dealing. We can sense here the pride of the newly appointed chief. Then he followed it by reminding the king of Ammon about how Yahweh had delivered them from the might of Egypt. ‘They came from Egypt.' Not many nations could say that. It was a part of history, and what Yahweh had done in delivering them from Egypt was widely known in the area. Let him think about that! Then they had travelled through the wilderness seeking a home. But when they arrived at Edom, Edom would not help them, and neither would Moab. Every word is loaded as he depicts how Israel were wronged.
His aim here was to put Moab in the wrong. They had refused to help Israel and had made life difficult for them, even though Israel had promised to refrain from attacking them, recognising them as related tribes holding their land under Yahweh's good hand (Deuteronomy 2:9). This was base ingratitude and demonstrated that they actually deserved worse than they got. Thus they had no case against Israel. It was the other way round. There is more detail here than in Numbers 22 where no messengers to Moab are mentioned, but it spoke of what was Moses' general practise (Numbers 20:14; Numbers 21:21) and he was presenting it in a way that put Moab clearly in the wrong. There was nothing here that could be specifically denied.
Note the use of ‘Israel' as subject of an active verb, very rare in Judges apart from in this speech. His aim was to depict Israel on a high level as a nation and not simply as a group of confederate tribes. The stronger he could show Israel to be the more likely that they would finally succeed. And there is possibly there too a hint that he now saw them as his people.
Then he went on to point out that not only had Moab or Ammon no right to the land in dispute but that their god Chemosh had actually handed it over to Sihon and the Amorites (Numbers 21:29). And that Israel had obtained it from the latter by right of conquest. Thus the land belonged by right of conquest to the people of Yahweh Who had dispossessed the Amorites.
But first he wanted to put Moab now even more in the wrong.