When it is painful to remember the past, it is better to simply repent of what had been bad, and think no more about it. In order not to despair or be enfeebled by it, 'remember the examples of God's great mercies to great sinners. The main thing: do not condemn, do not envy, know yourself and be with God.'
He Who before our offence forbids us to sin, after our offence ceases not from waiting for us to repent, He Whom we have rejected calls after us. We have turned away from Him, but He has not turned away from us.
One day, a young monk came to see an elder and asked him, 'What must I do, Father? I fall continuously in the same sin.' The elder replied, 'If you fall into sin, get up and do penance.' Monk: 'And if I fall again?' Elder: 'Then get up and repent of your sin again.' Monk: 'But until when?' Elder: 'Until your death.'
If the main goal of the repentant sinner should be total, light-bearing and blessed communion with God, then the main hindrance to this is the existence of the passions still active and working in him - the virtues being as yet unsealed in him - and the unrighteousness of his powers. Therefore his main work upon conversion and repentance should be the uprooting of the passions and sealing the virtues - in a word, correcting himself.
The Lord commands all men to repent (Matt. 4:17), so that even the spiritual and those making progress should not neglect this injunction and fail to give attention to the smallest and most subtle errors.
Remember, O my soul, the terrible and frightful wonder: that your Creator for your sake became Man, and deigned to suffer for the sake of your salvation. His angels tremble, the Cherubim are terrified, the Seraphim are in fear, and all the heavenly powers ceaselessly give praise; and you, unfortunate soul, remain in laziness. At least from this time forth arise and do not put off, my beloved soul, holy repentence, contrition of heart and penance for your sins.
By holy baptism original sin is expunged, as also sins committed before baptism. It also eliminates the violent power sin has over us till rebirth; it gives us the grace of the Holy Spirit by which we are united with God in Christ, and we receive power to subdue and conquer sin. For the simple reason that we are not delivered from the struggle with sin, we cannot be entirely free from sin during the whole of our earthly life, and even the righteous man may fall seven times (i.e. often) and rise again by repentance, says Scripture (Prov. 24:16). He falls on account of his weakness and limitations, because he does not always notice sin which subtly and imperceptibly rears its head from his fallen nature, and which is artfully and imperceptibly offered and suggested by fallen spirits. Repentance becomes his secure possession, his constant weapon, his invaluable treasure. By repentance the righteous man maintains his fellowship with Christ. He is healed by repentance from the wounds caused by sin.
Whoever repents sincerely is prepared to withstand any sorrow: hunger and homelessness, cold and heat, illness and poverty, humiliation and banishment, lies and slander, for the soul seeks God and does not concern itself with anything worldly, but instead prays with a clear mind.
True repentance consists of withdrawing from sin and nurturing hatred for it. For, lo, when someone says from his heart: I have hated deceit and been repelled by it - then God accepts him with joy.
First, one prays with the simplicity typical of beginners and by shedding copious tears. All this is due to the grace of God which is called purifying grace, which catches us like a fish-hook, and guides us towards repentance. For it is our God, Who is good in all and to all, Who finds us. He sees us. He invites Himself known to us first. Then we get to know Him, after He anoints us with His divine mercy. Hence, repentance, mourning, tears, and everything that happens to someone who repents, is all due to divine grace. This is purifying grace which cleanses man.