Eternal security, also known as "once saved, always saved" is the belief providing Christian believers with absolute assurance throughout their lives of their inevitable salvation. Its development, particularly within Protestantism, has given rise to diverse interpretations, especially in relation with the defining aspects of theological determinism and libertarianism, and the significance of personal perseverance.

Predestination, in theology, is the doctrine that all events have been willed by God, usually with reference to the eventual fate of the individual soul. Explanations of predestination often seek to address the paradox of free will, whereby God's omniscience seems incompatible with human free will. In this usage, predestination can be regarded as a form of religious determinism; and usually predeterminism, also known as theological determinism.