Midrash for Sotah 83:22

(Devarim 20:2) "And it shall be, when you draw near to the battle": I might think that this refers to the day of the joining of the battle; but (Ibid. 3) "And he shall say to them: Hear, O Israel, you are drawing near today to do battle with your foes" already refers to the day of the battle. How, then, am I to understand "And it shall be, when you draw near to the battle"? When they approach the boundary, the Cohein presents to them all of the conditions that follow.

(Devarim 20:3) "And he shall say to them "Hear, O Israel … against your foes": and not against your brothers: not Yehudah against Shimon and not Shimon against Yehudah, in which instance if you fell into their hands they would pity you, (viz. II Chronicles 28:8-15) — It is against your foes that you are going, who, if you fall into their hands, will not pity you!