This book is by  Hieromonk Gregorios, Elder of the Cell of St. John the Theologian, Koutloumousiou Monastery, Mount Athos. Trans. by Stelios Zarganes, Trim size 4x6, 52pp.

From the prologue---

Oftentimes we look at sin through two completely different lenses. Prior to committing a sin, we view it through the lens of insensibility, and thus consider the sin to be entirely natural. However, after it has been committed, we look at the same sin through the lens of despair, which magnifies it and leads us to the certain belief that we are beyond God’s forgiveness, thereby causing us to despair over our very salvation.

Christ, however, has revealed to us a sure way by which we can obtain the absolution of our sins, no matter how great the offense: by forgiving with all our heart those who have wronged us and loving them without regard to what they have done.