Here are a couple of dictionary definitions of Christianity:

* Christianity is an Abrahamic monotheistic religion based on the life and teachings of Jesus Christ as presented in the New Testament. Christianity is the world’s largest religion, with over 2.4 billion adherents, known as Christians. Christians believe that Jesus is the Son of God and the savior of humanity whose coming as Christ or the Messiah was prophesied in the Old Testament.

* The religion derived from Jesus Christ, based on the Bible as sacred scripture, and professed by Eastern, Roman Catholic, and Protestant bodies.

I suppose those are legitimate definitions.  Personally, I would define Christianity simply as those who know and follow the Lord Jesus Christ and the teachings of the Bible.  Of course, that encompasses much, when we consider the depth of the teachings of the scriptures.  First and foremost is the recognition and acknowledgement of who the Lord Jesus Christ is, and what He has done.

The Lord Jesus asked His disciples in Matthew 16:15, “Whom say ye that I am?”  That was such a foundational question and Peter’s answer was so important.  In verse 16, he answered, “Thou art the Christ, the Son of the living God.” To truly follow the Lord Jesus, we must see that He was not just a good teacher, a prophet, etc.  In the person of Christ, “God was manifested in the flesh.” (1 Timothy 3:16-NKJV).  We read in John 1:1 and 14, “In the beginning was the Word, and the Word was with God, and the Word was God.  And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth.”

In addition to acknowledging who the Lord Jesus Christ is, we must also understand and accept what He did in order to save us from the penalty of our sins.  Romans 10:9-10 tells us, “That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.”  The Lord Jesus Christ died on the cross to save us.  There, He suffered the wrath of God on our behalf.  He was buried and He rose again on the third day.  Salvation is offered to all people and comes from believing on the Lord Jesus Christ.  When asked by the Philippian jailer how to be saved, the Apostle Paul answered, “Believe on the Lord Jesus Christ and thou shalt be saved.” (Acts 16:31).

In seeking to answer your question about what Christianity is, I have answered by presenting the Gospel.  That is truly what Christianity is…the Gospel of Jesus Christ.  However, there is so much more to learn once we have put our faith in the Lord Jesus.  God’s Word, the Bible, teaches us so much about Him, it shows us how much He loves us, it gives us instruction for our daily lives, it tells us about the future of the world and about eternity itself.  The Bible is an inexhaustible book.  Its truths are essential, timeless, powerful, empowering, and comforting.  2 Timothy 3:16-17 tells us about the Bible, its origin and purpose.  It says, “All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, throughly furnished unto all good works.”

The word ‘Christian’ is found only three times in the Word of God.  The first time we read the word is in Acts 11:26, “And the disciples were called Christians first in Antioch.”  We notice that the disciples did not call themselves Christians, but those who saw them and their lifestyles were so impressed that their lives imitated that of Christ, that they began to call them Christians.  May we be as these disciples.  May our lives so reflect the life of Christ that others call us Christians.  (359.4)