June is traditionally dedicated to the Sacred Heart (presumably because the feast usually falls this month).
Here’s Karl Rahner on the topic (source, here):
The center of our hearts has to be God; the heart of the world has to be the heart of our hearts. He must send us his heart so that our hearts may be at rest. It has to be his heart. But it must not be the heart that embraces each and every thing in unfathomable unity. He must make us the center of our being a heart that is really the heart of the infinite God, and that nonetheless is a heart that is not everything, a heart that does not signify only one, a heart that is not only the ground of one. For the mortal fear over his ambiguous infinity and for the need of our hearts to depart from us, he has to let his heart become finite. He must let it become the unequivocality that is our life. He must let it enter into our narrow confines, so that it can be the center of our life without destroying the narrow house of our finitude, in which alone we can live and breathe.
And he has done it. And the name of his heart is: Jesus Christ! It is a finite heart, and yet it is the heart of God. When it loves us and thus becomes the center of our hearts, every need, every distress, every misery of our hearts is taken from us. For his heart is God’s heart, and yet it does not have the terrifying ambiguity of his infinity. Up from this heart and out of this heart human words have arisen, intimate words, words of the heart, words of God that have only one meaning, a meaning that gladdens and blesses.
This captures wonderfully the key theme of the devotion: in Jesus, divine love takes human form, and is expressed in a human way.
The devotion’s modern flourishing began in 17th century France, in a context where Janseinism, with its pessimistic and stern picture of God’s relationship to humanity, was rife. Against the Janseinist picture of a totally corrupt humanity trembling before a capricious deity, the Sacred Heart speaks of tenderness and compassion. However naff some of the imagery and popular piety that has developed in subsequent years (I had a friend who described it as ‘the cult of the glowing strawberry’), that message is very necessary in a context in which a frightened response to secularism leads far too many Catholics into stringency, rigorism, and reaction.