"I will bless the homes in which the image of my Sacred Heart shall be exposed and honored."
To a certain extent, the saying is true. "Out of sight, out of mind." We are creatures with five senses. We learn about the world through these five senses. We soon forget, and thus value less, what we don't readily see, or hear, or touch. For this reason, Holy Mother Church not only allows but recommends the proper use of sacred images as an aid to prayer and devotion. These images remind us of the holy people they represent, and help us to remember, love and imitate these holy people.
It is also true that, as the saying goes, some things are "hidden right under our noses." We see, but we do not remember. We pass the sacred image a hundred times in a day, and not once do we raise our minds and hearts to the person represented therein. But will we do better if there were no image at all?
Thus, we need both the image and the recollection. We need to pray when we see the image of the Sacred Heart on our walls or on our home altars. We need to remember whose Heart it is; what it stands for; how it suffered; how it loves; how it is a human heart like ours; how it is filled with divine love; how our hearts are meant to be filled with the same love. Doing so will do us a lot of good.
But there is a second motive. Jesus Himself attached a great promise to those who prayerfully keep this image exposed and honored in the home. He promises His own blessing.
Remember, this blessing is made to those who don't just "have" an image at home, but to those who 1) expose it and to those who 2) honor it. It should be visible and noticeable to all who live in and visit the house. It should be honored by regular acts of prayer and devotion.