It is to make us understand that all he has endured for us, He has endured just on account of the love with which His Heart was filled.
After showing to us the pains suffered in His Body, Jesus wishes us also the see the love of His most merciful, most faithful, most loving Heart, which inspired Him with the desire and the necessity of suffering for us.
Again, He has opened up for us His Heart in order that we might have a place of refuge in temptation, of consolation in sadness, of protection in trial, of safety in adversity and of light in doubt.
Indeed, to all who enter into this most beneficial Wound of His Heart, Jesus gives the sweetness of holy love, with salvation and eternal happiness.
This wound of the Sacred Heart of Jesus teaches us to pray unceasingly that our hearts may be so pierced with the spear of charity, that tears of compunction and of divine love may be as a river always flowing in our souls.
The Wound of the Side, which is the Wound of the Heart, therefore makes known to us the warm-hearted charity of Jesus Christ, a love which sheds an ineffable radiance over all His actions, all His words, and all His sufferings, filling them with unspeakable sweetness.
O most sweet Jesus in Heaven, shall I find my delight in Thy most sweet Heart?
How great, immeasurable, inexplicable, and incomprehensible is the joy of the elect who read in this most perfect book of Thy Heart the infinite love Thou hast for them.
They understand the fullness of Thy unfailing charity, which nothing can ever weaken, nothing ever destroy.
Oh, how happy and blessed is the mind to which Thou revealest so clearly and unconstrainedly the secrets of Thy most sweet Heart.
I will fall asleep in the Heart of Jesus, the source of true and supreme peace, the fountain whence springs and flows for my soul the endless tranquillity which will set me free for ever from the trials and sorrows of this life.
And since I must so soon leave this world, I place in Jesus my desires, my thoughts, and affections, by entering into His tender and loving Heart.
There I will hide myself as in a sepulchre, and will rest in a sweet sleep.
When, at length, I breathe my last, I will place my Heart in His opened side; I will confide my heart to His Heart.
Lanspergius [John Justus of Landsberg] (1489-1539): Ancient Devotions to the Sacred Heart of Jesus by Carthusian Monks of the XIV-XVII Centuries, pp. 39-41.