The Hebrew noun achdut derives from echad (one) and conveys the concept of unity — beings or things joined together as a single entity. Closely related to the Shema's declaration that "the LORD our God, the LORD is one."
The concept of achdut flows from the heart of Israel's theology: God is one, and His people are called to reflect that unity. Jesus prays that His disciples would be one even as He and the Father are one (John 17:21). The unity of the church is not organizational but organic, rooted in the shared life of the triune God.