The Holy Bible.
the Bible
The key to writing anything is communicating to the reader.
Jesus is Lord
Key practices of Christianity are reading the Bible. Praying to God. Worship in whatever form you may. Attending a church to fellowship with other believers.
That would be the new testament as without it Christianity wouldn't exist , merely Jewdeism.
The New Testament is the Christian scriptures.
Love
Christianity is popular because it is The Truth and key to heaven.
The first is being able to identify your audience. The second key to effective writing is establishing a purpose. The third key is formulating your message. The final key to effective writing is selecting your style and tone.
St. Paul, who spread Christianity as far as Rome. Constantine made Christianity the official state religion of the Roman Empire.
The key figure of Christianity is Jesus Christ. He’s the foundation of our faith. It’s all about His life, death, and resurrection. Jesus is the Son of God, sent to save us from our sins and give us eternal life. Everything in Christianity centers around Him—His teachings, His sacrifice on the cross, and His victory over death. When you understand who Jesus is and what He’s done for you, everything else in your faith journey falls into place.
A key's face is the top portion of the key where the letter, number, writing, or symbol is.