"Christ was faithful as a Son over His house whose house we are if we hold fast our confidence and the boast of our hope" (Heb 3:5-6). We are "Christ's body, and individually members of it" (1Co 12:27). "You are a temple of God" (3:16) "of the Holy Spirit who is in you" (6:19). This is contingent "if we hold fast our confidence" (Heb 3:6). The phrase "hold fast" doesn't sound modern but it does have the connotation of to fasten something which is to firmly attach securely in place. The NIV translates it to "hold on to our courage" (:6) which means it is highly recommended. The word "courage" seems to denote positive thinking, and "holding on" self effort. The NASB uses the word "confidence." But the spiritual interpretation is, "'Not by might nor by power, but by My Spirit'" (Zec 4:6). The author of Hebrews warns "do not throw away your confidence, which has great reward" (10:35). That shows at least that it is a matter of will power. The NIV expresses that "we hold firmly till the end the confidence we had at first" (3:14). To hold connotes grasping with your hand, and if you don't have a firm handhold, you might drop it. Does it imply that you might get tired of holding it and set it down? The starting point is marked as "the beginning of" (:14 NASB) or "at first" (:14 NIV). Then you are to "show this same diligence to the very end, in order to make your hope sure" (6:11 NIV) "so as to realize the full assurance of hope" (:11 NASB). We are to "hold unswervingly to the hope we profess" (10:23 NIV) "without wavering" (:23 NASB). You will receive "God's kindness, if you continue in His kindness; otherwise you also will be cut off" (Ro 11:22).
Another facet of perseverance is to "hold fast the word which I preached to you" (1Co 15:2). The understanding is in your mind, memory and comprehension. Paul applied this telling Timothy "continue in the things you have learned and become convinced of, knowing from whom you have learned them" (2Ti 3:14). Becoming convinced shows that it is not instantaneous but a process of study. "They observed the confidence of Peter and John . . . and began to recognize them as having been with Jesus" (Ac 4:13). Paul stated "we have boldness and confident access through faith in Him" (Eph 3:12) and "before Him" (1Jn 5:14). "Such confidence we have through Christ toward God" (2Co 3:4) and "great confidence in the faith that is in Christ Jesus" (1Ti 3:13). "We have confidence in the Lord concerning you" (2Th 3:4), "in you in the Lord" (Gal 5:10) and "am convinced in the Lord Jesus" (Ro 14:14). There is always an object associated with confidence. You are "convinced of this" (Php 1:25) and your "confidence is this" (2Co 1:12). Also you "confidently say" (Ac 2:29), "speak confidently" (Titus 3:8), and "make confident assertions" (1Ti 1:7). Furthermore, servants are to "speak Your word with confidence" (Ac 4:29) and you are to "speak to him [the king] also with confidence" (26:26). "By this, love is perfected with us, so we may have confidence in the day of judgment" (1Jn 4:17). "Abide in Him, so that when He appears, we may have confidence" (2:28) "because as He is, so also are we in this world" (4:17).