Hi:
Please explain to me why sometimes they do a different sign where they make a cross on the forehead and then the mouth and heart. When is this done and why? Thank you.
That form of the sign of the cross is done when the gospel is read at Mass. As mentioned, this symbolizes that the gospel is to be “in our minds, on our lips, and in our heart.”
I should note that originally, the sign of the cross was made on the forehead with one finger of the right hand (the large sign of the cross we know today came later, by the 4th century). A writer from the late 2nd to early 3rd century, Tertullian, claims that the custom dates back from the time of the apostles themselves:
At every forward step and movement, at every going in and out, when we put on our our clothes and shoes, when we bathe, when we sit at table, when we light the lamps, on couch, on seat, in all the ordinary actions of daily life, we trace upon the forehead the sign.
This was of course a sign of ownership: at baptism, Christ, through this sign of victory, laid his hand on the one being baptized, who received the cross traced on the forehead just as in antiquity slaves had a mark of ownership branded or tattooed on their foreheads. The sign of the cross on the forehead thus meant that one belonged to Christ. (You might also note that in the book of Revelation, we have two kinds of people: those who were sealed for God in their foreheads and those with the mark of the beast on their foreheads.)
We first hear of the custom of people signing themselves on the forehead after the deacon greets them in the 9th century. About a century later, we learn that all those present (now including the deacon) made a cross on the forehead and the breast whenever the words “Jesus said” come up. By the 11th century, people now signed themselves on the forehead, mouth and breast like we do today. A liturgist from that time known as Johannes Beleth explained the custom thus: “I am not ashamed of the gospel [the forehead was thought at that time to be the seat of shame]; I confess it with my lips and in my heart.” People at the time also signed themselves whenever the gospel reading ended, which is explained as a protection against the Enemy who tries to take the seed of the Word of God out of the hearer’s hearts (cf. Luke 8:12), although this custom never survived.
