It is "whose house we are, if we hold fast our confidence and the boast of our hope firm until the end" (Heb 3:6). "Now faith is the assurance of things hoped for, the conviction of things not seen" (11:1). We can have confidence if we're assured in our faith and have a conviction of what we're convinced of. When you are assured about something you know enough of the facts about it so that you can predict its behavior. It must be logical so that you can depend on its performance. You must feel good about it to place your faith in it. In fact, "faith is the assurance of things hoped for" (Heb 11:1). If your hope in something is well-founded based on evidence and how confident you feel about it then assurance is produced which represents faith in something. It is "the wealth that comes from the full assurance of understanding" (Col 2:2). To understand is to know. But there is the starting point where "we were dead in our transgressions" (Eph 2:5). Then there is "the beginning of our assurance" (Heb 3:14). Next, God makes "known to us the mystery of His will" (Eph 1:9) "resulting in a true knowledge of God's mystery that is, Christ Himself" (Col 2:2). It is so "you may stand perfect and fully assured in all the will of God" (4:12). Then "we will know by this that we are of the truth, and will assure our heart before Him" (1Jn 3:19). In their desperation "men's hearts were failing them for fear . . . [of what was] coming on the earth" (Lk 21:26 KJV) and God's solution is, "'Cease striving and know that I am God'" (Ps 46:10). Scripture has been written "so that you may know that you have eternal life" (1Jn 5:13). "This is eternal life, that they may know You, the only true God, and Jesus Christ whom You have sent" (Jn 17:3).
God "gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life" (Jn 3:16). "I give eternal life to them" (Jn 10:28). I've heard many people ask how does one comprehend eternal life? The Father sent Christ "into the world so that we might live through Him" (1Jn 4:9). "He is able also to save forever those who draw near to God through Him" (Heb 7:25). "The testimony of God is this, that He has testified concerning His Son" (1Jn 5:9) and "that God has given us eternal life, and this life is in His Son" (:11). "The one who believes in the Son of God has the testimony in himself" (:10) and "he who has the Son has the life" (:12). Your confidence is predicated on "that you may stand perfect and fully assured" (Col 4:12). But you don't stand on what you have personally figured out all by yourself. It is "He who began a good work in you" (Php 1:6) by way of "His calling and choosing you" (2Pe 1:10). His "great mercy has caused us to be born again" (1Pe 1:3). There is deliberation to it because "whoever will call on the name of the Lord will be saved" (Ro 10:13). It is "what I have entrusted to Him" (2Ti 1:12). "After listening to the message of the truth, the gospel" (Eph 1:13) "'everyone who has heard and learned from the Father, comes to Me'" (Jn 6:45). Paul states "you are saved, if you hold fast the word which I preached to you unless you believed in vain" (1Co 15:2). It is "on the basis of faith in His name" (Ac 3:16) and a choice to "repent and return" (Ac 3:19) in "repentance toward God and faith in our Lord Jesus Christ" (20:21).