John Calvin Commentary Deuteronomy 20:2

"And it shall be, when ye draw nigh unto the battle, that the priest shall approach and speak unto the people," — Deuteronomy 20:2 (ASV)

And it shall be, when you have come near. God commits the duty of exhortation to the priests when the time for conflict has arrived. But we gather from the expressions used that this passage is supplementary to the First Commandment, for it means nothing more than that the priest should encourage the Israelites to confidence. The ground for this confidence is declared to be the help of God in preserving and constantly protecting the Church, which He has once redeemed.

Moreover, He forbids their fears not with just one word, but heaps many together: "Let not your hearts faint, fear not, and do not tremble, neither be you terrified." By this we are reminded how difficult it is to cure that evil—fear—which in so many different ways assails and disturbs our minds, so that they do not rest in God. And surely, we all experience being troubled by such various trials that we need manifold remedies for the establishment of our faith.

We must also observe the familiar representation of God’s presence: that He goes together with His people to save them—that is, if they are exposed to danger not by their own fault, but by the unjust aggression of their enemies.