Devotion to Joseph’s heart has traditionally revolved around a devotion to all three hearts of the Holy Family, rather than a devotion unto itself*, however, recently a love and devotion just to his heart has been growing.
As the foster father of God, he’s the best example of living out good fatherhood (apart from God himself, of course), and he’s the patron of Chastity and Purity, living authentically and fully as the spouse of Mary, while upholding and protecting her perpetual virginity.
And through that, he points always to Mary, and both of them point to Jesus.
Joseph is the mans’ man. As a carpenter in the first century, he would have been more like a burly contractor than a fine craftsman. Most of the work would have involved building houses and public buildings, cutting down and shaping your own lumber.
Joseph isn’t some frail old man. He was a worker, knowing the daily grind. His words are not recorded in the Bible, but his love for Mary and Jesus have won for him the title Patron of the Universal Church.
He is perhaps the most relatable Saint, living a life completely hidden and unknown.
His heart is covered with the lily, symbolizing purity, and on fire like the hearts of Mary and Jesus, so passionately in love with God and us that it cannot be contained – it bursts into flames.
*Interestingly, there have been two apparitions of St Joseph in the past century (which have been found valid by their respective bishops) that speak into a devotion specifically for his heart. However, as private revelations, they don’t need to be believed by all faithful, and I don’t know if I agree to all parts. However, as I was reading them I was struck with how I might be reacting very similarly to Catholics before various Marian dogmas were instituted such as her Immaculate Conception who were like “what, that doesn’t make sense” and then the Pope validifies it and it’s part of our faith forever on the same level of truth as the Trinity. So we’ll see where those apparitions take us.