מדרש על סוטה 83:8

(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.