Making the sign of cross at start of Gospel

I notice before reading the Gospel that the pastor is cross himself three times, once the forehead, once on the lips, and once over the heart. Why?

This practice began between as early as the 9th century. It is the outward sign that correspond to a prayer that silently say. “May the Word of the Lord be in my mind, on my lips, and in my heart. Amen.” We find similar thoughts in Psalm 19:14 and Romans 10:8-17.
With this prayer, I acknowledge my dependence upon the Lord in proclaiming and even reading the Gospel.