Galatians 3:20 (KJV) states, "Now a mediator is not a mediator of one, but God is one." This verse speaks to the important theological concept of the mediator between God and humans, and the oneness of God.

In the context of the broader passage in Galatians, the apostle Paul is addressing the issue of the role of the Mosaic Law in relation to the promise of God to Abraham and the coming of Jesus Christ. Paul emphasizes that the Law was given through a mediator, Moses, but the promise was given directly by God. In this verse, he underscores the uniqueness of God as the one who makes and fulfills His promises. The verse also emphasizes the singularity of God, in contrast to the polytheistic beliefs prevalent during that time.

The theme of mediation between God and humans is central to various parts of the Bible, particularly in the Old Testament. The Israelites often relied on mediators, such as priests and prophets, to communicate with God and intercede on their behalf. This verse teaches that God, in His oneness, did not need a mediator to establish His promise to Abraham or to bring about the fulfillment of that promise through Jesus Christ.

The concept of mediation is also echoed in the New Testament, particularly in the person of Jesus Christ. In 1 Timothy 2:5 (KJV), it is written, "For there is one God, and one mediator between God and men, the man Christ Jesus." This verse further reinforces the idea that Jesus serves as the ultimate mediator between God and humanity, reconciling us to God and interceding on our behalf.

The oneness of God is a fundamental belief in Christianity, rooted in the doctrine of the Trinity – the understanding that God exists as one being in three persons: the Father, the Son (Jesus Christ), and the Holy Spirit. This verse in Galatians emphasizes the unity and singularity of God, affirming that He alone is the source of His promises and the fulfillment of those promises.

The symbolism in this verse lies in the contrast between the mediator of the Mosaic Law and the direct involvement of God in His promise to Abraham. It highlights the divine sovereignty of God and His ultimate authority in establishing and fulfilling His covenant.

Furthermore, this verse serves as a reminder to believers of the unique role of Jesus Christ as the mediator between God and humanity. It underscores the significance of Jesus' sacrificial death and resurrection, through which He provides access to God for all who believe in Him.

In conclusion, Galatians 3:20 (KJV) offers a profound insight into the nature of God as the singular source and fulfiller of His promises. It also points to the central role of Jesus Christ as the mediator between God and humanity. This verse encourages believers to place their trust in the oneness and sovereignty of God, and to recognize the unique mediation of Christ in reconciling us to God.