The Eucharist is the sacrifice of the Body and Blood of our Lord Jesus who instituted it for us. He did so in order to perpetuate the sacrifice of his cross throughout the ages until he should come again. In so doing he entrusts to his Church a memorial of his death and glorious resurrection.

Our Lord instituted the Eucharist when he celebrated the Last Supper with his apostles on Holy Thursday. He took bread and wine and offered them as his body and blood. This preceded his sacrifice on the cross on Good Friday. Jesus asked that his followers repeat this in memory of him, “Do this in memory of me” (1 Col 11:24). Faithful to that instruction the Church, especially on a Sunday (the day of the Resurrection), gathers to thank God and make present again the sacrificial memorial of Jesus who is truly present in the Eucharist.

The Eucharist is ‘the source and summit of the Christian life’. It is also known as the ‘Most Blessed Sacrament’ because all the other sacraments are orientated towards it. In it Christ associates the People of God with his sacrifice of praise and thanksgiving. By this sacrifice he pours out the graces of salvation on his Body which is the Church.

"The Eucharist is the efficacious sign and sublime cause of that communion in the divine life and that unity of the People of God by which the Church is kept in being. It is the culmination both of God's action sanctifying the world in Christ and of the worship men offer to Christ and through him to the Father in the Holy Spirit."
[Catechism of the Catholic Church, n.1325]

‘Thanksgiving’ is the literal meaning of Eucharist. The sacrament is a sacrifice of praise in thanksgiving for the work of creation. The Church offers her gratitude to God for all his benefits. This sacrifice of praise to the Father is offered through Christ and with him.

Eucharist is also a memorial in the sense that it makes present the sacrifice that Christ offered once for all on the cross to his Father. The sacrificial character of the Eucharist is evident from the words of Jesus at its inception: “This is my body, which is given for you…This cup is God’s new covenant sealed with my blood, which is poured out for you.” (Luke 22:19-20) The sacrifice on the cross and the Eucharistic sacrifice are one. The victim and the person offering it are identical – our Lord Jesus. Only the manner differs: the blood on the cross and the unbloody sacrifice in the Eucharist.

Finally, Jesus is truly present with us in the Eucharist. This is affected by transubstantiation which means that the bread and wine are transformed into the body and blood of Jesus. This change is brought about through the Eucharistic prayer, the words of Jesus (spoken by the priest) and the action of the Holy Spirit. Although the bread and wine retain their outward appearances - known as the 'Eucharistic species' - their substance has been altered.

By the consecration the transubstantiation of the bread and wine into the Body and Blood of Christ is brought about. Under the consecrated species of bread and wine Christ himself, living and glorious, is present in a true, real, and substantial manner: his Body and his Blood, with his soul and his divinity (cf. Council of Trent: DS 1640; 1651)
[Catechism of the Catholic Church, n. 1413]

Hence, the sacramental significance of the Eucharist can be summarized thus:
We must therefore consider the Eucharist as:
- thanksgiving and praise to the Father;
- the sacrificial memorial of Christ and his Body;
- the presence of Christ by the power of his word and of his Spirit.
[Catechism of the Catholic Church, n.1358]