This is one of the five points of Calvinism: the doctrine that anyone who is saved will remain so forever. Once saved, always saved. Thus, whoever God, for his own reasons, has elected will be saved and will remain saved.
PERSEVERANCE OF THE SAINTS
Meaning of PERSEVERANCE OF THE SAINTS in English
English glossary of religious terms. Английский глоссарий религиозных терминов. 2012