“many people even as the sand that is on the seashore.” To the five senses, this is a very dangerous force, but to Yahweh they are no threat.
“with very many horses and chariots.” The enemy had a well-equipped army, but God had told Israel not to accumulate horses (Deut. 17:16), without God’s help, they were not what won the battle (Ps. 33:17). Pharaoh’s chariot force did not bring him victory over Israel either (Exod. 14:17-28). Yahweh’s help brings victory and safety (Ps. 127:1). God commanded Israel to burn the chariots and make the horses ineffective for battle (Josh. 11:6). This would prevent Israel from trusting too much on physical things.