The Holy Mass is the highest form of worship.
The four aims of the Mass are to
adore God,
thank Him,
ask for forgiveness and
ask for our needs.

Two Parts

The Mass is comprised of two major and distinct, though related parts, namely
Liturgy of the Word and Liturgy of the Eucharist. One centers around the Bible, and other, around the bread and wine. However, both form one single act of worship. They are not independent of each other. What is proclaimed in the Liturgy of the Word is celebrated in the Liturgy of the Eucharist. Christ is present in both parts; first in His word, then in His Eucharistic action.
Christ said that man does not live by bread alone, but by every word that comes from the mouth of God. This word is our food before the Eucharistic bread: we receive Christ in the Sacred Readings before receiving Him in Holy Communion.

Liturgy of the Word

The purpose of the readings and the homily is to proclaim the Word of God, which has the power to change our lives. We are not simply to listen, but to respond to what is being proclaimed.

The purpose of the Liturgy of the Word is not information, but transformation; not merely to tell what God has done in the past, but what he continues to do today; not merely to instruct, but to lead to worship. Worship is not something we do for God; rather it is our response to what he has done for us.

The Liturgy of the Word lead us to respond to that word by sacrifice in the second part of the Mass.

Liturgy of the Eucharist : Meal and Sacrifice

Family and friends like to enjoy each other's company through having meals together, eg family dinners, lunches, birthday parties, picnics etc. It is not surprising then that Jesus chose a meal to be close to us. The prototype of this Eucharistic meal was the Passover meal when the Jews recalled their deliverance from slavery to freedom through God's intervention.

In Holy Comm-union (community union), everyone is united with Jesus and with each other.

The Eucharist is the same sacrifice of Jesus offered once and for all, re-presented (made present) for us who were not at Calvary under the sacramental sign of the consecrated bread and wine of the Eucharist.
The sacrifice at Calvary was bloody, the sacrifice at Mass is not.

We are God's children and by faith and baptism share in Christ's priesthood.
In the Mass we join our High Priest, Jesus in offering the Sacrifice of His Body and Blood. With the whole Church we unite the offering of ourselves and of all created things with Christ's offering to the Father. We adore God, we thank Him, we atone for our sins and we ask Him for help.

In the Jewish Passover, the unblemished lamb is sacrificed and eaten by family members. The Body of Jesus is also eaten by the family members of the community during Holy Communion.

Nourishments

We eat to get nourishments and to live.
The Mass nourishes us with the Word of God (first part, Liturgy of the Word) and the Body and Blood of Christ (Holy Communion) when Christ comes to our souls to give us a fuller share in His Sacrifice and unite us more closely to Himself and to one another.

When we eat food, the food is transformed into our beings. When we eat the Body and Blood of Christ under the form of bread and wine, Jesus transforms us into Himself.

The Real Presence

When the species (the bread and wine) are consecrated by a priest or bishop, "This is my body, ... This is my blood, ..." Jesus becomes really and truly present. We call this the Real Presence.

It is no longer bread and wine, but really Jesus Himself.
The substance (what the thing is) of bread and wine is changed into the Body, Blood, Soul, and Divinity of Jesus, even though we can still see and taste the accidents (what we see or taste) of bread and wine.
Traditionally, this is called transubstantiation.

It is not symbolic, but Jesus is really present.

"Very truly, I tell you, unless you eat the flesh of the Son of Man and drink His Blood, you have no life in you. Those who eat my flesh and drink my blood have eternal life, and I will raise them up on the last day." (John 6:53-54) This passage cannot be understood in a figurative way. In the biblical world, when the words "to eat the flesh and drink the blood" were used metaphorically, they meant to destroy someone, either by slander or by doing physical harm. (See Isaiah 49-26; Psalm 27:2.)

This is precisely why the Jews murmured at Jesus' words and why his disciples were shocked. They knew the phrase could only be taken literally. Jesus did not correct any misunderstanding on the part of the crowd or his disciples who walked away after He said these Words. (John 6:66) He simply reminded them that it is necessary to have God's Spirit to be able to accept such a teaching. (John 6:63.)