20 Come, my people, enter your chambers,
and shut your doors behind you;
hide yourselves for a little while
until the fury has passed by.
21 For behold, the Lord is coming out from his place
to punish the inhabitants of the earth for their iniquity,
and the earth will disclose the blood shed on it,
and will no more cover its slain.
-Isaiah 26:20-21
Courage is by and large a Christian virtue. God has given you family, neighbors and a people, and you must defend them if the situation calls for it. The same goes in warfare, for when God makes you a soldier you must fight valiantly: this is how He brought the children of Israel into the Promised Land after all, strengthening Joshua and his men to deal out punishments to the Canaanites.
But that said, fear is also a Christian virtue - more properly, fear of the Lord. When God decides to pour out His wrath, you *hide.* Isaiah insinuates that the faithful will have to hide from God's wrath the same way that they hid from the angelic destroyer during the Passover. This is not cowardice, but holy fear, knowing full well that you will become a collateral casualty if you put on airs of bravery while God lashes out at the wicked. Even when Christ returns, we may do well to hide while He slaughters those who hate Him; then He will come find us and bring us home.
We worship a God who is loving and merciful. But we also worship a God whose angry side we never, ever, ever want to see. When Judgment comes, even if you think you want to see it for some personal satisfaction, don't - in that moment, hide. When God tasks us with fighting we are made strong; when God does the fighting, we are reminded of how small we are.