We normally read three lessons
1st from the writings - normally Old Testament or Acts,
The Psalm re read together antiphonally
2nd from the Epistles (letters to the early church), and
3rd from one of the four Gospels (the stories of Jesus)
Normally the Priest or Bishop presiding over the Eucharist will commission (send in the apostolic sense) the reader of the Gospel to proclaim the Gospel in the midst of the people.
It reminds us that the Gospel is the peoples book, the peoples story, about the peoples messiah, and this story is told among the people.
It reminds us that we too are sent into the midst of the people with who we share our lives to live and proclaim the good news.
We normally sing a hymn as the Gospel is brought down amongst the people, and it is customary to stand and attend (face the reader), very much as the ancient people stood for the Passover meal, as they prepared for the journey to the promised land.