What is the significance for Catholics in signing our forehead, mouth (lips) and heart (breast) before the Gospel

During the Liturgy of the Word during Mass, prior to the holding the Holy Gospel the priest will silently prays with the following prayer, "Cleanse my heart and my lips, almighty God, that I may worthily proclaim your holy Gospel", or if it is a deacon to proclaim the Gospel, then the priest will bless him the following words, "May the Lord be in your heart and on your lips, that you may proclaim his Gospel worthily and well, in the name of the Father and of the Son and of the Holy Spirit". Next when priest/deacon opens the Holy Gospel and says "The Lord be with you", and the congregation respond, "And with Your Spirit". 

Then the priest/deacon says, "A reading from the Holy Gospel according to ....", and the congregation acclaim saying, "Glory to you, O Lord" whilst making the sign of the cross with his thumb on the Holy Gospel and on his forehead, mouth (lips), and heart (breast), which everyone in the congregation does at the same time. While signing of the three cross, the congregation should silently in the pray these words. "May the Word of the Lord be on my mind, on my lips, and in my heart". On feast days or solemnities, the priest/deacon will then incenses the Holy Gospel before he starts reading. All this is done just before the proclamation of the Holy Gospel at Mass.

After reading of the Gospel ends, the priest pronounces the acclamation, "The Gospel of the Lord", and the congregation replies, "Praise to you, Lord Jesus Christ". The Priest kisses the Holy Gospel, silently saying "Through the words of the Gospel". 

Next is the homily where we sit and listen as the priest explains what message of the Gospel, what Jesus was trying to share with us and how we can live this out in our lives.

Jesus is knocking at the door of our heart, waiting to get in each and every time we hear or listen to the Gospel.

The signing of three crosses before the proclamation of the Gospel signifies as follows:

• The signing of cross on the forehead that we understand the Gospel.
• The signing of cross on the mouth that we will proclaim Gospel.
• The signing of cross on the heart that we will take and keep the Gospel to heart, and put it into practice, and in with charity.