Calvin's Commentaries, Vol. 4: Harmony of the Law, Part II, tr. by John King, [1847-50], at sacred-texts.com
1. When thou goest out to battle against thine enemies, and seest horses, and chariots, and a people more than thou, be not afraid of them: for the LORD thy God is with thee, which brought thee up out of the land of Egypt.
1. Quum egressus fueris ad praelium contra hostes tuos ac videris equitatum, currus, et populum majorem te, non metues ab illis: quia Jehova Dens tuus tecum est, qui te eduxit e terra AEgypti.
2. And it shall be, when ye are come nigh untothe battle, that the priest shall approach and speak unto the people,
2. Et quum occurreritis ad praelium, accedet sacerdos ad populum,
3. And shall say unto them, Hear, O Israel; ye approach this day unto battle against your enemies: let not your hearts faint; fear not, and do not tremble, neither be ye terrified because of them;
3. Ac dicet illis, Audi Israel, vos occurretis hodie ad praeliandum cum hostibus vestris: ne mollescat cor vestrum, neque timeatis, neque terreamini, neque paveatis a facie eorum:
4. For the LORD your God is he that goeth with you, to fight for you against your enemies, to save you.
4. Quoniam Jehova Deus vester incredit vobiscum ad praeliandum pro vobis contra hostes vestros, et ad servandum vos.
1 When thou goest out to battle. This law also, which concerns their political government, is a Supplement to the First Commandment, enacting that they should carry on their wars under the auspices of God, and, trusting in His help, should follow Him as their leader. For it behoved them to give this proof of their piety, so as to look to God not less in war than in peace, and not to rest their hopes of safety on anything but the invocation of His name. Whence we gather that the worship of God should be by no means passed over in civil and earthly government; for, although its direct object is to preserve mutual equity between men, yet religion always ought to hold the first, place. The sum, therefore, is that, amidst the very clang of arms, they must not be in such confusion as not to recognize that they are under the guardianship of God, or to lose the confidence they will be safe in reliance on His power. He does not, however, encourage them rashly to engage in war, but takes it for granted that there is a legitimate cause for it; because this would be a gross abuse of God’s name, to seek a prosperous issue from Him, when we are engaged in anything contrary to His command. But He forbids them to fear, although the enemy should be superior in horses, in multitude, and in all their warlike array; and in these words He reminds them that they would not be liable to suffer defeat, because they were not supplied with abundance of chariots and horses; for we have lately seen that not even their kings were permitted to collect the forces in which the Gentile nations gloried; and therefore, lest the consciousness of their weakness should make them afraid, God declares that His strength would be a sufficient safeguard to them. And without question that passage in Ps 20:7, is taken from hence, “Some trust in chariots, and some in horses; but we will remember the name of the Lord our God.” On which score Isaiah reproves the people, because, refusing the waters of Shiloah, they long for great and rapid rivers; viz., as he elsewhere explains it, because they trust in the horsemen of Egypt. (Isa. 8:6, Isa. 31:1.) But we must observe upon what their security is to be founded, viz., because the people ought to hope that the same Divine power would be with them to the end, which their fathers had experienced when they were redeemed from Egypt.
2 And it shall be, when ye are come nigh. God commits the duty of exhortation to the priests, when the time of the conflict shall have arrived. But we gather from the expressions used that this passage is supplementary to the First Commandment, for it contains no more than that the priest should encourage the Israelites to confidence, the ground of which 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 in one word only, but heaps many together, “let not your hearts faint, fear not, and do not tremble, neither be ye 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, that they should not rest in God. And surely we all experience that we are troubled by such various besetments, that we have need of manifold remedies for the establishment of our faith. We must observe, too, the familiar representation of the presence of God, that He should go together with His people, to save them, viz., if they should be exposed to danger not by their own fault, but by the unjust aggression of their enemies.