If you perceive something good and great on earth, think of heaven, and it will appear small and insignificant to you. If you encounter something terrible, think of hell and you will laugh at it. If sensual desire tempts you, think of the fire and consider that sinful pleasure is contemptible and not even a true delight.
If even the fear of worldly laws exerts such great power that it keeps us from bad deeds, how much more so when we think of eternity, of unceasing punishment, of everlasting torment. If the fear of an earthly ruler already keeps us from so much evil, how much more will the fear of the eternal King do so!
But how can we keep this fear constantly in our hearts? We can do so if we always listen to Holy Scripture.
If even the sight of a corpse powerfully impresses us, why should the thought of the eternal, unquenchable fire of hell remain without effect, or the worm that never dies? Truly, if we always thought of hell, we would not easily fall into it! That is why GOD has threatened us with the punishment of hell:
If the thought of it were not beneficial, He would not have done so. Because the remembrance of the punishments of hell produces such great effects, God has given us the threat as a salutary remedy. Let us not forfeit the great benefit that arises from contemplating hell, but always think of it: at breakfast no less than at dinner! Conversations about entertaining things do not benefit the soul; they only rob it of its strength. Discussions about serious and shocking truths take away all frivolity and flightiness and lead the soul from thoughtlessness and distraction to seriousness and prudence.
Conversations about spectacles and jokes bring no advantage to the soul, but only make it more lustful and bolder. Whoever meddles curiously in the affairs of others and interferes in everything often endangers his own affairs precisely because of this. But whoever makes hell the subject of conversation need not fear any danger for his soul:
No, it is of the most salutary influence for it. Yet you fear that such talk will annoy others? If you keep silent about it, will you thereby extinguish the fire of hell? Or do you ignite it by speaking of it? By no means! It will continue to burn, whether you speak of it or not. Therefore, you must speak of it unceasingly if you do not want to end up in hell yourself. A soul that fears hell will not easily fall into sin. There is an invaluable admonition—may you never let it slip from your memory! It is: “Remember your last things, and you will never sin for eternity!” [Sir 7:36]
Whoever always thinks with fear and trembling of giving an account will not easily fall into sin. For the fear dwelling in the heart banishes all that is sinful from it. If even a conversation about hell seizes and shakes us so powerfully, how much more must the thought of hell, if it dwells not only temporarily but constantly in our hearts, purify the soul—more purifying than any fire.
Source: John Chrysostom (344-407) Homilies on the Second Letter to the Thessalonians 2,3