Judith makes Holofernes think he will win against Israelites.

In the last chapter we were kept in suspense as to what Judith would do, because she seemed to have detected to the Assyrians. If that was her plan to pretend to be a traitor and later double cross the Assyrians, then she would need to lie and thus going against her usual moral self.
However, it is amazing how things unfolded here. She told the Assyrians the blatant truth in a way that the Assyrians thought the outcome is good for them. That is true in a way, as Judith said, if the Israelites continue in their sin, then the Israelites would be defeated. Holofernes, the Assyrian general liked this part, but what he did not ponder too much on was that if there Israelites repented, then the Assyrians would be defeated.

Judith 11 
Then Holofernes said to her, “Take courage, woman, and do not be afraid in your heart, for I have never hurt anyone who chose to serve Nebuchadnezzar, king of all the earth. ² Even now, if your people who live in the hill country had not slighted me, I would never have lifted my spear against them. They have brought this on themselves. ³ But now tell me why you have fled from them and have come over to us. In any event, you have come to safety. Take courage! You will live tonight and ever after. ⁴ No one will hurt you. Rather, all will treat you well, as they do the servants of my lord King Nebuchadnezzar.”

Judith Explains Her Presence

⁵ Judith answered him, “Accept the words of your slave, and let your servant speak in your presence. I will say nothing false to my lord this night. ⁶ If you follow out the words of your servant, God will accomplish something through you, and my lord will not fail to achieve his purposes. ⁷ By the life of Nebuchadnezzar, king of the whole earth, and by the power of him who has sent you to direct every living being! Not only do human beings serve him because of you, but also the animals of the field and the cattle and the birds of the air will live, because of your power, under Nebuchadnezzar and all his house. ⁸ For we have heard of your wisdom and skill, and it is reported throughout the whole world that you alone are the best in the whole kingdom, the most informed and the most astounding in military strategy.

⁹ “Now as for Achior’s speech in your council, we have heard his words, for the people of Bethulia spared him and he told them all he had said to you. ¹⁰ Therefore, lord and master, do not disregard what he said, but keep it in your mind, for it is true. Indeed our nation cannot be punished, nor can the sword prevail against them, unless they sin against their God.

¹¹ “But now, in order that my lord may not be defeated and his purpose frustrated, death will fall upon them, for a sin has overtaken them by which they are about to provoke their God to anger when they do what is wrong. ¹² Since their food supply is exhausted and their water has almost given out, they have planned to kill their livestock and have determined to use all that God by his laws has forbidden them to eat. ¹³ They have decided to consume the first fruits of the grain and the tithes of the wine and oil, which they had consecrated and set aside for the priests who minister in the presence of our God in Jerusalem—things it is not lawful for any of the people even to touch with their hands. ¹⁴ Since even the people in Jerusalem have been doing this, they have sent messengers there in order to bring back permission from the council of the elders. ¹⁵ When the response reaches them and they act upon it, on that very day they will be handed over to you to be destroyed.

¹⁶ “So when I, your slave, learned all this, I fled from them. God has sent me to accomplish with you things that will astonish the whole world wherever people shall hear about them. ¹⁷ Your servant is indeed God-fearing and serves the God of heaven night and day. So, my lord, I will remain with you; but every night your servant will go out into the valley and pray to God. He will tell me when they have committed their sins. ¹⁸ Then I will come and tell you, so that you may go out with your whole army, and not one of them will be able to withstand you. ¹⁹ Then I will lead you through Judea, until you come to Jerusalem; there I will set your throne.^[a] You will drive them like sheep that have no shepherd, and no dog will so much as growl at you. For this was told me to give me foreknowledge; it was announced to me, and I was sent to tell you.”

²⁰ Her words pleased Holofernes and all his servants. They marveled at her wisdom and said, ²¹ “No other woman from one end of the earth to the other looks so beautiful or speaks so wisely!” ²² Then Holofernes said to her, “God has done well to send you ahead of the people, to strengthen our hands and bring destruction on those who have despised my lord. ²³ You are not only beautiful in appearance, but wise in speech. If you do as you have said, your God shall be my God, and you shall live in the palace of King Nebuchadnezzar and be renowned throughout the whole world.”