The following is taken from Fr. Garrigou-Lagrange's Reality: A Thomistic Synthesis.
Why did Jesus suffer so much, seeing that the least of His sufferings offered with such love would superabundantly suffice for our salvation?
In answer, let us look at our Savior's sufferings from three points of view; our own, His own, and that of God the Father.
a) We need to be Illumined on how to receive the greatest testimony of love, accompanied by the highest example of heroic virtue. Now there is no greater love than giving life for those we love.
b) Christ Himself must fulfil His redemptive mission in the highest manner. Now, as priest, no victim but Himself was worthy. And to be a perfect holocaust He must be completely victim, in body, in heart, in a soul "sorrowful unto death." Further, having the fullness of charity, and being both viator and comprehensor, He necessarily suffered with boundless intensity from mankind's sins taken on Himself, seeing in these sins both the offense against God and the cause of the loss of souls.
c) God the Father willed by this road of suffering and humiliation to give our Savior the grandest of victories, a threefold victory, over sin, over the devil, over death. The victory over sin was gained by the greatest of all acts of charity, victory over the devil's disobedience and pride by the supreme act of obedience and the loving acceptance of the lowest humiliations, victory over death, the consequence and punishment of sin, by the glorious external sign of the two preceding victories, a victory culminating in His resurrection and ascension. "Christ humbled Himself, becoming obedient unto death, even to death on the cross. Hence God exalted Him, and gave Him a name above every name, a name before which all kneel... while every tongue, to the glory of God the Father, confesses that Jesus Christ is the Lord."