Why Do I Need to Be Baptized?

John the Baptist baptizing Jesus Christ

To answer that question we should start with who our Heavenly Father is - He is a perfect being.  He lives in heaven and that is perfect.  With that in mind - would we (imperfect beings) really fit in without being pure ourselves? No, we make mistakes, we do wrong things, and we know they are wrong because we can feel it.  We must be clean of these mistakes in order to be with Him in heaven. Because God is perfect He has a perfect love.  So He sent His Son Jesus Christ to redeem us from our imperfect and impure state so we could return and live in heaven.  Jesus performed the Atonement which paid the price for our sins and mistakes.  In order for us to take full advantage of the gift of the Atonement we must have faith and turn to God with all our heart (also known as repenting).  Just believing in Christ is not using the Atonement (just as believing the cookie on the counter is actually there does not get you any closer to eating it).

Young man being baptized by immersion just as the Savior was (Matthew 3:16)

We must act to use the atonement.  Many of the actions that get us closer to using the Atonement, such as having faith, reading scriptures, praying, keeping the commandments, etc. can and are being done around the world, but Baptism has certain requirements: The scriptures show that man must be called of God to act in His name (Hebrews 5).  Not just anyone could do God's work (Jeremiah 23:21, Matthew 7:21-29, Acts 19:1-6 - Paul rebabtized converts of an unauthorized teacher [The John spoken of in v. 3 could not have been John the Baptist because they did not know what the Holy Ghost was, and John the Baptist always taught about that]).  The same principle applies today, and that authority of God is on the Earth today.  It has been restored!  We must be baptized by someone holding the Priesthood Authority of God to keep a commandment (Matthew 3:13-15, John 3:5), and be cleansed of sin (Acts 22:16).