Praise be to Allaah.
If it is decreed that you should be a soldier fighting in the army against the Jews or any other kuffaar, then make your intention purely for the sake of Allaah in your fighting against them, and have the intention of supporting Islam and the Muslims, and making the word of Allaah supreme and the word of kufr the lowest. In this way, your fighting will be for the sake of Allaah. It was reported that a man asked the Messenger of Allaah (peace and blessings of Allaah be upon him): “A man who fights for the sake of booty, a man who fights for the sake of fame and a man who fights for the sake of status – which of them is fighting for the sake of Allaah?” The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The one who fights so that the word of Allaah will be supreme is the one who is fighting for the sake of Allaah.” (Agreed upon, from the hadeeth of Abu Moosa al-Ash’ari, may Allaah be pleased with him). (Al-Bukhaari, 3/206; Muslim, 3/1512-1513).
And Allaah is the Source of Strength. May Allaah bless our Prophet Muhammad.