When Our Lord appeared to St Margaret Mary, He revealed the secrets of His Sacred Heart. What does His Heart look like? What does the tradition of the Church say about Its symbolism?

The Flame issuing forth from the Sacred Heart shows us Our Lord’s Great Charity.
Permit me O my Jesus, to kiss Your wounded side, and to enter into Your Divine Heart, where you may destroy my malice in the flames of its charity, transform me totally into Yourself, and fill my soul with Your Divine love.
Fr Ignatius of the Side Wound of Jesus, CP
The Cross in His Sacred Heart shows that Our Lord loved his Cross as it was the instrument of our salvation, and that He did so from the beginning of His life.
Sweet Jesus of Nazareth,
You gave us heaven’s reward
Upon the cross. Why won’t we take heed?
His fresh wounds did bleed so terribly.
(Art. 92, Lutel wot hit any mon hou love hym haveth ybounde)
The Crown of Thorns around His Heart show us that His whole life was hedged around by trials and sufferings, which He embraced for the love of us.
How much He loved us! How ungrateful we are for all that he has done for us. Can we not suffer for his sake?
Hail Jesu! thine holy head
With sharpe thornes was be-weaved;
…
Hail Jesu! thy painful death
Be my shield and my red
From devil’s harm.
Hail! sweet Jesu, thy mercy!
For thine pains sore,
Noble heart it is my law to love thee
Whose heart-blood was shed for me.
(Anonymous, Worlde’s blisse, have good day!)
The rays surrounding His Sacred Heart show forth the divinity of Jesus.
Every movement of the Sacred Heart comes from the hypostatic union of the divine nature with the human nature. The hypostatic union is the union of the divine nature and human nature of Christ in one individual existence (hypostasis). The Sacred Heart is not perturbed or agitated by any external disturbance because of our Lord’s perfect submission to the will of God the Father. This is a perfect tranquility. Live within it to be untroubled, imitating it. Look at it in its perfect tranquility. When He was suffering in agony from the reproaches and lashes of others, it was in perfect tranquility.
The lance which pierces the Heart and creates the wound in the side of the Heart is the lance of Longinus. This shows us the depth of His love for us.
It was his Will… to show us that His love was not quenched by death. Therefore He permitted that His sacred side should be opened with a spear after His death, so that we might behold His Divine Heart pierced for love of us.
Fr. Ignatius of the Side Wound of Jesus, CP
The sword pierced his soul and came close to his heart, so that he might be able to feel compassion for me in my weaknesses.
St. Bernard
The wound in the side of the heart was opened for many reasons.
First, to give the outpouring of the Precious Blood to enable the sacraments, and thus ultimately the Church. Our Christian life was thus born from the side wound of Christ.
Second to give a place for us to enter into, a refuge from all demons, a place filled with grace and perfect love.
Sweet in the opening of His Side; for indeed that opened Side has revealed to us the treasures of His goodness, His Heart and His Heart’s love for us.
St. Anselm
… a door opened for us, through which we might enter, and behold the ever-living, ever-burning love of the Heart of Jesus, even after death…. Those wounds which bleed no longer because every vein is emptied of the last drop of its blood, tell us loudly how great, how excessive, is the love of God for us, since it has reduced Him to such a condition for our sake…. Is there anyone to be found, who can contemplate that open side, that tender, wounded, loving Heart, without feeling himself obliged to return love for love? Enter, my soul, enter into the burning furnace of the tender Heart of Jesus, enter it frequently in spirit, and there your incredible hardness of heart will be softened, and your icy coldness warmed. You will be inflamed with holy love for your God. Behold the last drop of warm blood issuing from that sacred Heart… for the good of those who inflict the wound upon Him ([St Longinus])! Permit me O my Jesus, to kiss Your wounded side, and to enter into Your Divine Heart, where you may destroy my malice in the flames of its charity, transform me totally into Yourself, and fill my soul with Your Divine love.”
Fr. Ignatius of the Side Wound of Jesus, CP
O great, precious and loving Wound of my Saviour, You have penetrated more deeply than all the others, and are opened so wide that all the faithful can enter in! O Wound from which flow unlimited and endless precious blessings, Wound of the Side inflicted last, but become nevertheless the most celebrated! Whosoever drinks deeply from the holy and divine source of this Wound, or takes even a few drops, will forget all his ills, will be set free from the thirst for fleeting and vile pleasure, will be inflamed with the love of eternal and heavenly things, and filled with the unutterable sweetness of the Holy Spirit. Then will flow into his soul “a fountain of water springing up into life everlasting. (Jn 4:14).
Enter, O my soul, enter into the right Side of Your crucified Lord, enter through this blessed Wound into the centre of the all-loving Heart of Jesus, pierced through and through out of love. Take your rest in the clefts of the Rock sheltered from the tempests of the world. Enter into your God! Covered with herbage and fragrant flowers, before you lies the path of life, the way of salvation, the bridge which leads to Heaven.
The Heart of Jesus is the City of Refuge in which we are safe from the pursuit of the enemy; the City of Refuge which defends us from the wrath of an angry Judge. This Heart is the inexhaustible fountain of the oil of mercy for truly penitent sinners. This Heart is the source of the divine river springing up in the midst of Paradise to water the surface of the earth, to quench the thirst of the dry and barren human heart, to wash away sins, to extinguish the impure fires of concupiscence, to regulate the flights of the imagination and to allay the fierceness of anger. Draw near then and take the draught of love from this fountain of the Saviour, in order that you may no longer live to yourself, but in Him Who was crucified for you. Give your heart to Him Who has opened His Heart to you. Give not your heart to the world, but to Christ. Give it not to vain worldly wisdom, but to the eternal Wisdom. Where can you rest more peacefully, dwell more securely, or sleep more sweetly than in the Wounds of Christ crucified for you? ….
Jesus our King, Saviour of the faithful, Who wanted Your holy Side to be opened by the point of a ruthless lance, I humbly and fervently beseech You to open to me the doors of Your mercy, and allow me to enter through the large Wound of Your adorable and most holy Side, into the interior of Your infinitely loving Heart, so that my heart may be united to Your Heart by an indissoluble bond of love. Wound my heart with Your love. Let the soldier’s spear penetrate my breast. Let my heart be opened to You, to You alone, and closed to the world and the devil. Protect my heart, and arm it against the assaults of my enemies by the sign of Your Cross.
Amen.
by a Carthusian