"All you who are thirsty, come to the water! You who have no money, come, buy grain and eat; Come, buy grain without money, wine and milk without cost!" (Isaiah 55: 1)

"All you who are thirsty,
come to the water!
You who have no money,
come, buy grain and eat;
Come, buy grain without money,
wine and milk without cost!"  (Isaiah 55: 1)

The offer of salvation is universal and free.  Everyone is invited. Although it is free, it is not cheap.  Juicy rich food is promised and not "wretched food."  Choice wine is made available for this Banquet of the Lamb.

Grain, water, wine and milk are types of the Eucharist.

In Numbers 21: 4 -5, the Israelites rejected the food given to them by God.
"From Mount Hor they set out by way of the Red Sea, to bypass the land of Edom, but the people’s patience was worn out by the journey; so the people complained against God and Moses, “Why have you brought us up from Egypt to die in the wilderness, where there is no food or water? We are disgusted with this wretched food!"  (Numbers 21: 4 - 5).

The wretched food they complained about is the manna, a type of the Eucharist.  In the Eucharist, Jesus Christ offers us Himself to be our food and drink.  The Church describes the Eucharist as "the sum and summary of our faith. 'Our way of thinking is attuned to the Eucharist, and the Eucharist in turn confirms our way of thinking."  (Catechism of the Catholic Church #1327)

The Church commemorates the gift of the Eucharist in the Solemnity of Corpus Christi (the Most Holy Body and Blood of Christ)