Deuteronomy 31:6

Be strong and courageous, do not be afraid or tremble in dread before them, for it is the Lord your God who goes with you.  He will not fail you or abandon you.”

Covenant with God means He does the fighting for us, and we do the believing and trusting for our part. Knowledge of God and His promises make us able to stand and withstand the trials.  Our faith is our strength, and the Word of God is the covenant language that backs it up.  We believe, and therefore we speak, and the mountains will move.