Thanks for your question and for watching the live stream of my sermon, "Spirit, Soul, and Body" (https://player.vimeo.com/video/399711729?autoplay=1). As we saw from this study, most often Scripture uses the words "spirit" and "soul" synonymously—that is interchangeably with the same basic meaning. Only in a few instances in Scripture, do we see a distinction (e.g. 1 Thess. 5:23; Heb. 4:12, etc.). When this distinction is used, the contrast is between the inner part of us that focuses on heavenly things as opposed to the inner part of us which just focuses on physical feelings and sensations. When they are used synonymously, both can be applied to our state after death (cf. 1 Pet. 3:19; Rev. 6:9; Eccl. 12:7). Salvation in Christ is said to save the "soul" (Jas. 1:21; 1 Pet. 1:9, 22) or the "spirit" (1 Cor. 5:5; Heb. 12:23). If the soul or spirit can be said to be saved, it necessarily infers that those spirits or souls who are not saved are "lost" (cf. Matt. 16:26; 1 John 4:3). It is appropriate, therefore to speak of "lost souls" or "lost spirits" when speaking of those outside of Christ. I hope this answers your question.