So, this user on Reddit has been posting some amazing infographics explaining Catholic theology, especially the connection between Old & New Testaments.

Let me present 3 wonderful infographics from "Defense of Sanity." https://www.reddit.com/user/Defense-of-Sanity/

The Eucharist is seen in the commands to eat given in the OT: Melchizedek tells Abraham, the Passover celebration, the Mana in the Desert & Ezekiel's Scroll.
The Eucharist is also parallel to the fall but reversing it.

The Gospel of Luke links Mary to the Ark of the Covenant through overshadowing, dancing in her presence, etc.
Jesus represents the three items in the old ark: bread, word, and priest.
This shows us that Mary is pure.

Finally, an infographic on the Pope.
He is the Rock in Matthew 16, he is given the keys like Isaiah was, he has authority, and has a line of succession. Jesus designed his Church to have a chief steward: The Pope.

Purgatory is a purification to enter Heaven, not some intermediate place.
Sin has 2 effects and confession/absolution only cleanses us of the more serious effect leaving purgatory to clean the less dramatic effect.
We can find references to Purgatory in what Paul & Jesus said

The 1st Christians believed:
The Eucharist was Literally Jesus
You confess to a priest
You baptize infants
Purgatory exists
Mary was sinless

We can know that God exists from reason alone, without faith. Atheists are the unreasonable ones.

The Bible indicates that priests can forgive sins and all the early Church Fathers agreed with the sacrament of confession.

Having priests who perform the sacraments for us actually emphasizes, not refutes the idea that Jesus is the one mediator.

The Old Testament, New Testament, and the Early Church all indicate that the Church of Jesus should have priests.

The "Once-saved-always-saved" idea doesn't correspond to a full understanding of scripture and how Jesus indicates he saves us.

If we believe any ancient document is an accurate record, we should believe that the Bible is accurate. It more manuscripts and closer than pretty much any other ancient text.

If we look at the historical and scientific evidence, it seems clear that Jesus' death and resurrection happened. Here's a summary of the evidence.

If we look at the test of Scripture, it is clear that Jesus did not have any full blood siblings and Mary was a perpetual virgin both before and after Jesus' conception and birth.

The foundations and reasons for priestly celibacy seem to go back to the early Church and even the New Testament.

If we look at the NT scriptural citations and those of the early Church, they clearly seem to accept the Septuagint which included the 7 books Protestant Bibles lack. Augustine himself quoted all seven of these books in his writings as canon.

The parallelism with circumcision in the Old Testament, the practice of baptizing whole households in Acts, & the practice of the early Church all point to infant baptism. Denying baptism till a moment of conscious belief is a later tradition not rooted in what the apostles did.