What does the consideration of our Lord's leaving the world entail?
It entails four things: the Passion, the death, the burial, and the descent into hell (XLVI.-LII.).
Why did our Lord suffer His Passion and death on the Cross?
First of all to obey His Father, who had thus determined in His divine plans; and because, knowing intimately these divine plans, He knew that the Passion was to be the masterpiece of the wisdom and love of God, whereby salvation was secured to men (XLVI. 1).
Did the sufferings of our Lord Jesus Christ surpass all other conceivable sufferings?
Yes, because the human nature of our Lord in its sensibility and sensitiveness was exquisite and the most perfect possible; and although in the heights of His soul He possessed and enjoyed for ever the beatific vision, no ray of this splendour was allowed to enter the darkness of His sufferings to bring light and consolation to Him; further, He bore all the sins of men upon His shoulders which His sufferings were to wipe out (XLVI. 5, 6).
Next - The Catechism of the Summa - Tertia Pars - XX. OF OUR BLESSED LORD'S LEAVING THIS WORLD: OF HIS PASSION AND HIS DEATH; OF HIS BURIAL (B)