Definition and Context:
The concept of "living sacrifices" is primarily derived from the New Testament, specifically from the Apostle Paul's epistle to the Romans. In Romans 12:1, Paul exhorts believers to present their bodies as "a living sacrifice, holy and pleasing to God," which he describes as their "spiritual act of worship" . This idea marks a significant shift from the Old Testament sacrificial system, where sacrifices were typically animals offered on an altar for atonement and worship.

Old Testament Background:
In the Old Testament, sacrifices were central to the worship and religious life of Israel. The Law of Moses prescribed various offerings, including burnt offerings, grain offerings, peace offerings, sin offerings, and guilt offerings (Leviticus 1-7). These sacrifices were physical, involving the shedding of blood and the death of the sacrificial animal, symbolizing atonement for sin and dedication to God.

New Testament Transformation:
With the advent of Jesus Christ, the sacrificial system underwent a transformation. Jesus is described as the ultimate sacrifice, the "Lamb of God, who takes away the sin of the world" (John 1:29). His death and resurrection fulfilled the requirements of the Law, rendering the old sacrificial system obsolete for atonement purposes (Hebrews 10:1-18).

In this new covenant context, Paul introduces the concept of believers themselves becoming "living sacrifices." This is not a call for physical death but a metaphorical expression of total dedication and consecration to God. It involves offering one's entire being—mind, body, and spirit—in service and obedience to God's will.

Theological Significance:
The call to be a living sacrifice is deeply theological, emphasizing the believer's response to God's mercy. Romans 12:1 begins with "Therefore," indicating that this exhortation is a response to the preceding chapters, where Paul expounds on God's grace, mercy, and the redemptive work of Christ. The believer's life, therefore, becomes an act of worship, a continuous offering in gratitude for God's salvation.

Practical Implications:
Being a living sacrifice involves a transformation of life and character. Romans 12:2 continues, "Do not be conformed to this world, but be transformed by the renewing of your mind" . This transformation is both inward and outward, affecting how believers think, act, and interact with the world. It calls for a rejection of worldly values and an embrace of God's will, which is "good, pleasing, and perfect" (Romans 12:2).

Spiritual Worship:
The phrase "spiritual act of worship" (Romans 12:1) underscores that true worship is not confined to rituals or ceremonies but is a lifestyle of obedience and service. This aligns with Jesus' teaching that true worshipers will worship the Father "in spirit and truth" (John 4:23).

Conclusion:
The concept of living sacrifices encapsulates the essence of Christian discipleship. It is a call to live a life wholly devoted to God, reflecting His holiness and love in every aspect of life. This sacrificial living is both a response to God's grace and a testimony to the transformative power of the Gospel.