Where in Scripture, do we find that the Jewish Passover becomes the Mass?

Today is Holy Thursday and this is what Jesus did on Holy Thursday. He transformed the Jewish Passover into the Christian Mass.

Matthew 26:16 And from that time he sought opportunity to betray him. 17 Now the first day of the feast of unleavened bread the disciples came to Jesus, saying unto him, Where wilt thou that we prepare for thee to eat the passover? 18 And he said, Go into the city to such a man, and say unto him, The Master saith, My time is at hand; I will keep the passover at thy house with my disciples.

Note that Jesus prepares the disciples for a Passover. But this is what He says during that Passover:

26 And as they were eating, Jesus took bread, and blessed it, and brake it, and gave it to the disciples, and said, Take, eat; this is my body. 27 And he took the cup, and gave thanks, and gave it to them, saying, Drink ye all of it; 28 For this is my blood of the new testament, which is shed for many for the remission of sins.

Jesus prepared the disciples for a Passover. But during that Passover, celebrated the Mass. St. Paul obviously understands this:

1 Corinthians 5:7 Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us:

So what does it mean that YOU are now UNLEAVENED?

St. Paul is using "leavening" in a metaphorical sense. To understand the metaphor, you must go to the Old Testament. God would not accept any offering with leaven:

Leviticus 2:11 No meat offering, which ye shall bring unto the Lord, shall be made with leaven: for ye shall burn no leaven, nor any honey, in any offering of the Lord made by fire.

Before the Passover, the Jews were supposed to clean house by throwing out all leavening.

Exodus 12:15 Seven days shall ye eat unleavened bread; even the first day ye shall put away leaven out of your houses: for whosoever eateth leavened bread from the first day until the seventh day, that soul shall be cut off from Israel.

Why? Because leavening is a form of putrefaction. Yeast is a germ. Have you ever heard of a “yeast infection”?

This is why “leavening” is associated with sin. Because sin can corrupt the body, the way that yeast “corrupts” its host. When St. Paul says, “Purge out therefore the old leaven”, he is referring to sin. We must purge out the sin in our lives and become one bread, one body with Christ. And Christ is unleavened. He is totally without sin.

Hebrews 4:15 For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin.

And before we eat of the Eucharist, our Passover, we must purge out the sin in our lives by examining our conscience, repenting of our sins and going to Confession. Because we don’t want to eat of the Bread of Life with sin on our souls:

1 Corinthians 11:28 But let a man examine himself, and so let him eat of that bread, and drink of that cup. 29 For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord's body. 30 For this cause many are weak and sickly among you, and many sleep.

When we unite ourselves to Christ in the Holy Eucharist, we must be a pure lump, that ye may be a new lump, as ye are unleavened, without sin.

Christ is the True Passover. And long ago, it was prophesied that Christ would become the Pure Offering acceptable to God:

Malachi 1:11 For from the rising of the sun even unto the going down of the same my name shall be great among the Gentiles; and in every place incense shall be offered unto my name, and a pure offering: for my name shall be great among the heathen, saith the Lord of hosts.

To Conclude

On Holy Thursday, Jesus Christ celebrated a Jewish Passover and transformed it into the Christian Mass.