Put on the full armor

"Why has the Lord permitted us to be defeated today by the Philistines?"  (1 Samuel 4: 3)

All warfare prefigures spiritual warfare.  The Israelites did not ask for the blessings of God before they engaged the Philistines in battle.  If they done this, they would have learned that there was sin in the camp which they needed to deal with in the first place.

The Lord permitted them to be defeated because they  did not put on the full armor.

Before you go into Battle against Evil:

"Finally, draw your strength from the Lord and from his mighty power.
Put on the armor of God so that you may be able to stand firm against the tactics of the devil.
For our struggle is not with flesh and blood but with the principalities, with the powers, with the world rulers of this present darkness, with the evil spirits in the heavens.
Therefore, put on the armor of God, that you may be able to resist on the evil day and, having done everything, to hold your ground.
So stand fast with your loins girded in truth, clothed with righteousness as a breastplate,
and your feet shod in readiness for the gospel of peace.
In all circumstances, hold faith as a shield, to quench all [the] flaming arrows of the evil one.
And take the helmet of salvation and the sword of the Spirit, which is the word of God.
With all prayer and supplication, pray at every opportunity in the Spirit.."  (Ephesians 6: 10 - 18)