Why did our lord Jesus Christ, While on the cross, say “Father, forgive them…�(Luke 23:34), and why did He not say, through His own authority, “your sins are forgiven..�?
On the cross, the Lord Jesus Christ represented mankind.
He represented all humanity in paying the wages of sin, in response to the Divine justice “ All we like have gone astray; we have turned, every one, to his own way; and the Lord has laid on Him the iniquity of us all� (Isaiah 53:6). For this reason, on the cross, he was “…a burnt sacrifice…a sweet aroma to the Lord� (Leviticus 1:9); He was also a sin offering, and a “Passover� (1 Corinthians 5:7)
Therefore, our Lord was offering atonement for our sins to the Father, and He offered this sacrifice, He said to the Father “forgive them�, or in other words, “I have satisfied the Justice that You, O Father, have demanded, and therefore, forgive them.’
Before the Father, our Lord spoke as an advocate on behalf of all humanity, and as a representative of every sinner, from Adam until the end of all ages.
In His intercession He was announcing His abdication of His rights toward; His crucifiers, those who condemned Him to die unjustly, those who falsely accused Him, and those who stirred the crown against Him without knowing what they were doing.
Although this is the case, our saviour, in other circumstances, gave forgiveness by himself, as God.
In Mark 2:5, our Lord said to the man sick with palsy, “your sins are forgiven,� giving evidence of His divinity and His authority to forgive sins; He also said to the sinful woman in the house of Simon the Pharisee , “your sins are forgiven,�(Luke 7:48). His authority to forgive sins did not depart from Him on the cross, for He forgave the penitent thief on the right, and said to him “ …today you will be with me in paradise� (Luke 23:43), declaring our saviour’s forgiveness of the thief’s sins without which he could not enter into paradise.
This Q&A was found on Archangel Michael & St Bishoy Coptic Orthodox Church : http://www.stbishoy.org.au/modules/smartfaq/faq.php?faqid=42