You and I begin each day with confidence in several unchanging realities! We are confident our planet earth will continue to rotate at exactly the same speed that it has for millennia and thus time will move, and sunrise will happen right on schedule. Gravity will work as it always has, and after a few hours evening will arrive, and it will be the end of this day. But the truth is when it comes to most every other aspect of our lives today, we cannot be as totally confident. All around us the unexpected is happening all the time.
It was very much the same in the first century and therefore the apostle John was writing his first letter to raise confidence in those early Christians that God was reliable and their salvation, if authentic, is secure in Jesus Christ.