From '1 Samuel 7:1-17, we read of what happened between the Israelis and the Philistines. Then, God assigned prophets over His chosen Land Israel, and Samuel was the prophet as of the time. The Philistines was to engage in a battle with the Israelis, and they also had a greater army in terms of physical strength and could have conquered Israel, but due to the fact that Israel was in a covenant with God, they tapped into it through the Spiritual prophet Samuel, using sacrificial offering in the altar of God.
A sacrificial offering is what you lay down on the altar of God, which moves Him to act on your behalf when what you are facing is bigger than you humanly speaking. In our dispensation, it can come as worship, praise, prayers, holiness, money, material items, or anything at all as led by the "Holy Spirit". It is important to note that life is in phases and stages, and to get to the next phase, you've got to face some battles, and some times, these battles are bigger than us humanly speaking, so it's the sacrifice you lay down on the altar of God that would help you scale through. The universe functions in a principle of "Seed time and Harvest time", so it is what you've supplied to God as a sacrifice that would give you the ground on laying a demand out of it based on the Word of God. Most importantly, we should always know that everything we receive from God is by His Mercy and Grace, and nothing of our own self sufficiency.