The Purpose of His Holy Church?
Since the Church was established by the appointment of Yeshua, heir to the throne of David, a.k.a. Jesus the Christ and King of the citizens of Judea and those Israelites who followed His Ways then the purpose of the Church is His purpose. 
"To every [thing there is] a season, and a time to every purpose under the heaven:" Ecclesiastes 3:1
The Church has both a mission and a purpose. Like the human body it has many parts, many attributes, and many functions. It is part of the system of the Kingdom of Heaven. It is the body of Christ appointed by Him for His purposes.
"To what purpose [is] the multitude of your sacrifices unto me? saith the LORD: I am full of the burnt offerings of rams, and the fat of fed beasts; and I delight not in the blood of bullocks, or of lambs, or of he goats." Isaiah 1:11
The Purpose of His Holy Church is to serve the LORD God, YHWH, YaHWeHe, Johovah... Through obedience to His obedient Son, Jesus Christ, His anointed in spirit and in truth, who has appointed the Church to serve and feed His Sheep.
"But rise, and stand upon thy feet: for I have appeared unto thee for this purpose, to make thee a minister and a witness both of these things which thou hast seen, and of those things in the which I will appear unto thee;" Acts 26:16
The Church was created by Jesus the anointed King of the Nation of Judah which was the remnant of Israel and the Kingdom of David. It is the family of God on earth.
"And, behold, I purpose to build an house unto the name of the LORD my God, as the LORD spake unto David my father, saying, Thy son, whom I will set upon thy throne in thy room, he shall build an house unto my name." 1 Kings 5:5
Who are the Brethren of the household of the Lord?
And he stretched forth his hand toward his disciples, and said, Behold my mother and my brethren! For whosoever shall do the will of my Father which is in heaven, the same is my brother, and sister, and mother. Matthew 12:49, 50
Those who do the will of the Father in Heaven not just those who proclaim His name are the brethren of Jesus Christ and the brothers of His Holy Church. Many have taken His name in vain but those who are faithful to His Purpose are His Church.
Who is doing the will of the Father?
"For this purpose the Son of God was manifested, that he might destroy the works of the devil. Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God. In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother." 1 John 3:8...
Those born again of the Spirit of God will not seek to commit the sins of the adversary of God. They will neither stand between the Lord and His people nor will they let others stand between the People and our Father in Heaven. They will always seek to maintain and Entrance to the Kingdom of Heaven which they are to preach, is at hand.
"For so an entrance shall be ministered unto you abundantly into the everlasting kingdom of our Lord and Saviour Jesus Christ" 2 Peter 1:11
Is it enough to love one another?
"For if ye love them which love you, what reward have ye? do not even the publicans the same? And if ye salute your brethren only, what do ye more than others? do not even the publicans so? Be ye therefore perfect, even as your Father which is in heaven is perfect." Matthew 12:46,48
The Church strives in loving obedience and compliance to the will of God so that all men may see that which has been kept secret.They ae heralds of His Kingdom of God, making strait the way of the LORD.
"And to make all men see what is the fellowship of the mystery, which from the beginning of the world hath been hid in God, who created all things by Jesus Christ: To the intent that now unto the principalities and powers in heavenly places might be known by the church the manifold wisdom of God, According to the eternal purpose which he purposed in Christ Jesus our Lord:" Ephesians 3:9, 11
The purpose of His Holy Church is as it was in the beginning, is now and forever shall be.
May the brethren of His Holy Church be of service to the LORD God of Heaven and earth by serving you in your pilgrimage to discover the Truth, the Way and the Life, the Kingdom of God and His righteousness..