"But continue thou..."
"Hang in there," says Paul. The Christian life may involve much more than this simple admonition, but none of it is relevant if we stop putting it into practice. Christianity is more than creeds and crises. It's a criterion for life. It is not just a "life-style" that bends and molds to fit the current culture. Jesus said He was the "way, the truth, and the life." Then He said, "Follow me." That assumes persistence.
"...in the things which thou hast learned..."
You can only continue if you have first begun. Verse fifteen makes it plain that Timothy's knowledge of the Bible, as taught to him by his mother and grandmother, laid a foundation that culminated in his later faith in Jesus Christ. The former does not guarantee the latter; and the former without the latter only paves the way to hell with even less excuse. But no one can deny that early training in Spiritual matters, coupled with a godly example, is an advantage that money cannot buy and pedigree cannot obtain. And when the Seed springs forth into everlasting life, especially at an early age, there is no greater benefit in life. It is greatest reason why I consider myself to be a fabulously wealthy woman!
"...and hast been assured of..."
There comes a time, especially with young people reared in a Christian home, when what one has been taught will require personal assurance. To say that the Bible is true simply because our parents, pastor, or spiritual teachers says so, will never convince anyone else; and at some stage in your life, it will not convince you. This is not because the learned principles and values are necessarily questionable; it merely means they are valid enough to stand up to questions. Each of us has his or her own method of justifying what he or she believes. Some come to the Truth among the thinkers on Mars Hill (Acts 17:34); others rise from a hog pen to wend their way home to the Father (Luke 15:11-24); while a great host succumb to the Sprit of God under anointed preaching of the Word of God (Acts 2). The only thing that matters is that the questions find their answers in Jesus Christ. Whatever leads to Him, leads to life. That is where the assurance is found.
"...knowing of whom thou hast learned them."
We should always remember who taught us; and this is not as obvious as it may seem. In Timothy's case, it may have started with his mother and grandmother, but although he modestly leaves himself out of the equation, the apostle, Paul, played a great part in this young man's Christian life, as well. My own story is similar. Along with spiritual training at home, I had a godly pastor, teachers, and mentors who nurtured me through my walk of faith. But we should not stop there. In the final analysis, it is the Spirit of God who teaches us, according to John 14:26. And unless He does, no one else can. When one has had the benefit of learning from teachers with such credentials, it leaves little room for halting steps on the pathway of faith.
You and I as believers are on sure footing here, so there is no reason to stop or even hesitate.
Hang in there!