Father Dominic. in his sermons, tells us to always have the name of Jesus on our lips. What is the reason?

The name Jesus in Hebrew means: "God saves." The name of Jesus fully manifests the supreme power of the "name which is above every name" (Cf. Jn 12:28)."There is no salvation through anyone else, nor there is other name under heaven given to the human race by which we are to be saved"(Acts 4:12). The evil Spirits fear his name;In his name his disciples perform miracles, for the Father grants all they ask in this name(Cf. Acts 16:16-18;19:13-16; Mk 16:17; Jn 16:16). The name of Jesus is at the heart of Christian Prayer. All liturgical prayers conclude with the words "through our Lord Jesus Christ". The Hail Mary reaches its high point in the words "blessed is the fruit of thy womb Jesus." The Eastern prayer of the heart,the Jesus Prayer, says: "Lord Jesus Christ, Son of God, have mercy on me,a sinner." Many Christians such as St. Joan of Arc, have died with the one word "Jesus" on their lips.

The invocation of the Holy name of Jesus is the simplest way of praying.When the  the Holy Name is repeated often by a humble and attentive heart,the prayer is not lost by heaping up empty phrases, but holds fast to the word and brings forth fruit with patience. This prayer is possible at all times because it is the only occupation: that of loving God, which animates and transfigures every action in Christ Jesus. So, its one of the best things you can do to humbly repeat the name of Jesus at all times.[See CCC 430-435,2668]