Cogitationes Cordis ejus in generatione et generationem: ut eruat a morte animas eorum et alat eos in fame. * Exsultate, justi, in Domino, rectos decet collaudatio.

The thoughts of His Heart are to all generations: to deliver their souls from death and feed them in famine. * Rejoice in the Lord, ye just: praise becometh the upright.
(Introit from Psalm 32:11,19,1)

From a beautiful essay on today’s feast at Liturgia Latina:

The solemnity of the Sacred Heart sums up all the phases of the life of Jesus recalled in the liturgy from Advent to the Feast of Corpus Christi.

It constitutes an admirable triptych giving us in abridgment all the mysteries, joyous, sorrowful and glorious, of the Saviour’s life devoted to the love of God and men. This feast is indeed placed on a height from which may be contemplated the redeeming labours of the Saviour on earth and the glorious victories He will, by the working of the Holy Ghost, achieve in souls until the end of the world.

Coming after the feasts of Christ, this feast completes them, concentrating them in one object which is materially Jesus’ Heart of flesh, and formally the unbounded charity symbolised by this Heart. This solemnity therefore does not relate to a particular mystery of the Saviour’s life, but embraces them all; indeed the devotion to the Sacred Heart celebrates all the favours we have received from divine charity during the year (Collect), and all the marvellous things that Jesus has done for us (Introit, Tract, Alleluia). It is the feast of the love of God for men, a love which has made Jesus come down on earth for all by His Incarnation (Epistle), which has raised Him on the Cross for the Redemption of all and which brings Him down every day on our altars by transubstantiation, in order to make us benefit by the merits of His death on Calvary.

These three mysteries, which manifest to us the divine charity in a more special way, sum up the spirit of the feast of the Sacred Heart. It is ” His love which forced Him to put on a mortal body” (Hymn at Matins). It is His love which willed that the Sacred Heart should be pierced on the cross (Gospel and Communion), in order that from the wound should flow a spring (Preface) we might draw from joyfully (f at 2nd Vespers), whose water cleanses us from our sins in baptism and whose blood nourishes bur souls in the Eucharist. And as the Eucharist is the continuation of the Incarnation and the sacrifice of Calvary, Jesus asked that the feast should be placed immediately after the Octave of Corpus Christi.