No one should despair ever, even if he has committed many sins, but should have hope that, through repentance, he shall be saved.
From the Life of St. Synkletike
The Blessed Synkletike said: We should laud remiss and indolent souls who are easily exhausted in the struggle for good, as well as those souls who are easily discouraged and fall to despair. Indeed if such souls should display even the smallest good deed, we must praise it and marvel at it, giving them encouragement in their struggle for the good. Contrarily the most serious and greatest of their faults we must characterize, in front of them, as the least and unworthy of note. For the Devil, who wishes to destroy all things, or rather to succeed at our spiritual destruction, resorts to the following ruse. On the one hand, with accomplished and ascetic monastics, he tries to cover their sins and to make them forget them, so as to create pride in them. On the other hand, he constantly exposes the sins of neophytes—whose souls have not yet been strengthened in the ascetic life—before them, exaggerating these sins, so as to drive such neophytes to despair, until they abandon their ascetic efforts.
For this reason, then, these still irresolute souls we must care for with tenderness, reminding them continually of the boundless compassion and kindness of God. Among other things, we must emphasize that our Lord is merciful and long-enduring and that He annuls His righteous judgments against wrong-doers, as long as they surely repent.
To render this teaching of ours convincing, we will bring forth examples from Holy Scripture, which will reveal to the souls of our listeners the endless compassion of the Lord towards those who have sinned and repented. For example, let us recall that Raab was a prostitute, but was saved through her faith; St. Paul was a persecutor, but through repentance became a chosen vessel; and the thief who was crucified together with Christ on Golgotha, who had stolen and murdered, first opened the door of Paradise with one word of repentance: “Remember me, Lord, when Thou comest into Thy Kingdom.” Moreover, let us cite the instance of St. Matthew, who was appointed to the Apostolic ranks by the Lord and who, even though a former tax collector, relates the parable of the tax collector, as well as that of the Prodigal Son. In general, then, let us bring to mind all of the stories in this regard which emphasize the worth of repentance and which extol the compassion of God towards the repentant man.
On the other hand, we must correct those souls who are ruled by pride by providing them with greater examples, just as we give the weaker souls encouragement, so as not to be ruled by despair. Let us take an example from the work of the best gardeners, who, when they see that a plant is of small stature and sickly, water it profusely and care for it greatly, so that it will grow and be strong; while, when seeing in a plant the premature development of sprouts, they immediately trim the useless sprouts, so that the plant does not quickly wither. Likewise, physicians give rich nourishment to some patients, prescribing that they walk, while to others they give a strict diet and require them to remain at rest.