Any successful organization needs a meaningful reason for it’s existence. In most cases, "Purpose Statements" are developed by founders and leaders of organizations. There is no organization on the planet in which that MUST be true, than when it comes to the reason for the existence of the local church.
Colossians 1:18 tells us, “And he (Jesus Christ) is the head of the body, the church: who is the beginning, the firstborn from the dead; that in all things he might have the preeminence." Jesus, Himself, said, In Matthew 16:18, “...I will build my church; and the gates of hell shall not prevail against it." Jesus Christ is the Head and Builder of His local churches, therefore, He is the one Who declares the purpose of the local church, and He has declared our purpose quite plainly. When the devil tried to sidetrack Him from His purpose, Jesus said in Matthew 4:10, “Thou shalt worship the Lord thy God, and him only shalt thou serve.”
Then, as He ascended back to Heaven after His resurrection, He gave as His important parting words, His direction of purpose in Acts 1:8, “But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth." And, again, in Matthew 28:19-20, "Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you alway, even unto the end of the world. Amen."
Therefore, Jesus Christ, our Founder and Head has said our purpose is...
WORSHIP AND SERVE HIM BY PREACHING THE GOSPEL TO ALL NATIONS AND TEACHING THOSE WHO BELIEVE ON HIM.