What does 1 Samuel 2:4 mean?

Hannah changes the focus of her song from God's absolute holiness, power, and knowledge (1 Samuel 2:1–3) to how God uses that power among human beings. In short, when He chooses to act, He is the difference between victory and defeat. He determines success and failure. He is the ultimate power source behind all human efforts.

That "the bows of the mighty are broken" means the Lord can bring to a dead stop even the most fearsome armies and warriors. Breaking the bow was a picture of ending an enemy's ability to continue to make war. This imagery is used especially in the Psalms (Psalms 37:15; 46:9; 76:3).

At the same time, the Lord adds strength to those who are weak or stumbling. Hannah depicts God binding strength, as if it were a weapon or shield, onto the arms of those who are feeble. The picture is of God reversing fortunes and expected outcomes. We tend to size up two opponents and decide ahead of time that the one with the appearance of overwhelming strength will win. Hannah insists that the Lord can reverse that outcome in a moment.