Definition and Purpose:
An altar, in biblical terms, is a structure upon which offerings, such as sacrifices, are made for religious purposes. Altars are central to worship practices in the Bible, serving as a place of communion between God and His people. They symbolize the acknowledgment of God's sovereignty, the atonement for sin, and the dedication of one's life to God.

Old Testament Usage:
In the Old Testament, altars were integral to the worship practices of the Israelites. The first mention of an altar is found in Genesis 8:20, where Noah built an altar to the LORD after the flood and offered burnt offerings. Altars were constructed from earth or uncut stones, as instructed in Exodus 20:24-25: "You are to make an altar of earth for Me and sacrifice on it your burnt offerings and peace offerings, your sheep and goats and cattle. In every place where I cause My name to be remembered, I will come to you and bless you."

The patriarchs, such as Abraham, Isaac, and Jacob, built altars as acts of worship and covenant with God (Genesis 12:7, 26:25, 35:7). The most significant altar in the Old Testament was the bronze altar in the Tabernacle, later in the Temple, where daily sacrifices were made (Exodus 27:1-8). This altar was central to the sacrificial system, which foreshadowed the ultimate sacrifice of Christ.

New Testament Fulfillment:
In the New Testament, the concept of the altar takes on a spiritual dimension. Jesus Christ is seen as the fulfillment of the sacrificial system, rendering the physical altars of the Old Testament obsolete. Hebrews 13:10 states, "We have an altar from which those who serve at the tabernacle have no right to eat." This refers to the sacrifice of Christ, which provides believers with direct access to God.

The New Testament also speaks of the altar in a metaphorical sense. In Matthew 5:23-24, Jesus teaches about reconciliation, saying, "Therefore if you are offering your gift at the altar and there remember that your brother has something against you, leave your gift there before the altar. First go and be reconciled to your brother; then come and offer your gift." Here, the altar represents the place of worship and offering to God, emphasizing the importance of relationships and forgiveness.

Symbolism and Significance:
Altars symbolize various aspects of the believer's relationship with God. They represent sacrifice, worship, and covenant. The altar is a place of surrender, where individuals lay down their lives in service to God. Romans 12:1 urges believers to "offer your bodies as living sacrifices, holy and pleasing to God—this is your true and proper worship."

In Revelation, the altar is depicted in the heavenly realm, signifying the eternal worship of God by His people (Revelation 8:3-5). This imagery underscores the continuity of worship from the earthly to the heavenly, where the ultimate altar is before the throne of God.

Conclusion:
The altar, throughout Scripture, serves as a powerful symbol of worship, sacrifice, and communion with God. It points to the ultimate sacrifice of Jesus Christ, who fulfills the requirements of the law and opens the way for believers to approach God with confidence.