Not To Be Confused With
Assurance is the subjective confidence of salvation; perseverance/eternal security concern the objective fact that the saved are kept. One can be truly saved yet struggle for assurance, and traditions differ on whether assurance is normal, attainable, or of the essence of faith.
Rooted in 1 John ('that you may know that you have eternal life,' 5:13) and Romans 8:16 (the Spirit witnessing with our spirit). The Reformed and Wesleyan traditions prize it; the Catholic tradition is more cautious about certainty. It rests not on the strength of one's faith but on the One it trusts.