John Newton answers a question about 1 John 5:10. This is his conclusion:
…the hope of a believer is built upon a foundation that cannot be shaken, though it may and will be assaulted. It does not depend upon occasional and changeable frames, upon any that is precarious and questionable, but upon a correspondence and agreement with the written word. Nor does this agreement depend upon a train of labored arguments and deductions, but is self-evident, as light is to the eye, to every person who has a real participation of the grace of God. It is equally suited to all capacities. By this the unlearned are enabled to know their election of God, and "to rejoice with a joy unspeakable and full of glory." And the wisest, if destitute of this perception, though they may be masters of all the external evidences of Christianity, and able to combat the cavils of infidels, can see no real beauty in the truths of the Gospel, nor derive any solid comfort from them.
The whole letter is very insightful.