If something is very delicate and fragile, you’ll handle it with care and compassion. Human nature demands that God act toward it with sensitivity and compassion.
God is also “merciful” to us because we forget that we are created from earth; we forget that we are nothing and act as if we were gods. To such a person, one can only be patient and show mercy.
God is “long-suffering”. He exercises patience with us, because we are ignorant and rebellious; because we stubbornly resist Him. We are not interested in God because our attention is occupied with a life of fantasy and ego, our self-will.
God is “rich in mercy” because human sinfulness is as deep as the ocean. Mercy is God’s response to sin and the soul. In the words of the Hymn of Kassiani: “Who can count the multitude of my sins or fathom the abyss of Your judgments?” St Gregory Palamas writes, “Him alone, therefore, the Master and Creator of all, you should glorify as God and through love you should cleave to Him; before Him you should repent day and night for your deliberate and unintentional lapses. For He is compassionate and merciful, long-suffering and rich in mercy.”
 Psalms and the Life of Faith, Archimandrite Aimilianos of Simonopetra, Indiktos, pp 280-281.
Source: December 2015 – January 2016 Lychnos Edition