In Paul's second letter to Timothy, we learn this about Timothy: "that from childhood you have known the sacred writings which are able to give you the wisdom that leads to salvation through faith which is in Christ Jesus." This leads to those well-known words: "All Scripture is inspired by God and profitable for teaching, for reproof, for correction, for training in righteousness; so that the man of God may be adequate, equipped for every good work" (3:15-17).
What might those sacred writings have been? We get a glimpse from Paul's letter to the Romans: "For whatever was written in earlier times was written for our instruction, so that with perseverance and the encouragement of the Scriptures we might have hope" (15:4).
When Paul wrote his first letter to the Corinthians, in what we know as chapter 10, verses 1-12, we read a lengthy admonition with examples as to what to learn from the failures of the Israelites.
When Paul wrote of Timothy's knowledge of the sacred writings, clearly he meant the Old Testament. Now we have both the Old Testament and the New Testament.
Suppose, like Timothy, we have known the Scriptures--the 66 books which make up the Bible--from our childhood? Some of us have been fortunate, then, that our Lord has seen fit to use that knowledge to bring us His saving grace for many years.
When I was a child, He did this for me. But I wrestled with a lack of assurance. I "went forward" times without number and threw countless sticks on fires at Bible camps. I went to so many vacation Bible schools, church camps, even a Christian college, unsure.
Somewhere in there it occurred to me that I was still to some extent relying on my own actions/works and not fully on what Christ had done. It was only then that I began to experience assurance. It was not a matter of emotion, but reliance on what the Scriptures say. There are times of emotion, yes--joy--but those are not times I expect or rely on to confirm my salvation.
As Paul was inspired to write to Timothy: "All Scripture is inspired by God and profitable for teaching, for reproof, for correction, for training in righteousness" (2 Timothy 3:16).
There was some thought that, having assurance of salvation, one could go on spiritual "cruise control" through the rest of life. This is far from biblical.
In his letter to the Philippians, Paul wrote that we are to "work out [our] salvation with fear and trembling, for it is God who is at work in you, both to will and to work for His good pleasure" (2:12b-13); and in his letter to the Ephesians, "For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand so that we would walk in them" (2:10).
In his second letter, Peter provides us with a structure/direction for spiritual growth: "Grace and peace be multiplied to you in the knowledge of God and of Jesus our Lord; seeing that His divine power has granted to us everything pertaining to life and godliness, through the true knowledge of Him who called us by His own glory and excellence. For by these He has granted to us His precious and magnificent promises, so that by them you may become partakers of the divine nature, having escaped the corruption that is in the world by lust. Now for this very reason also, applying all diligence, in your faith supply moral excellence, and in your moral excellence, knowledge, and in your knowledge, self-control, and in your self-control, perseverance, and in your perseverance, godliness, and in your godliness, brotherly kindness, and in your brotherly kindness, love. For if these qualities are yours and are increasing, they render you neither useless nor unfruitful in the true knowledge of our Lord Jesus Christ. For he who lacks these qualities is blind or short-sighted, having forgotten his purification from his former sins" (1:2-9).