It is popular for the millennial generation and many others to say that you can't know the answer to important questions regarding your soul. The spirit of the age is uncertainty and tentativeness. To have a firm opinion on a matter of morality or spirituality is not considered socially acceptable. For some, having a firm opinion is unwise because of the trouble it can get you in. It's more popular to have questions and to have problems with different things, rather than to embrace a fixed truth. John the apostle does not think that way at all. Nor does he want his children to be that way.
In 1 John 5:18-21 we learn that you can have certainty. God desires that His people are not tossed about like a wave of the sea driven and tossed by the wind.
Please consider coming to our national conference: Repentance - The Reformation Continues - October 26-28 in Asheville NC.