Our purpose is to behold and be changed by the glory of God in Christ by faith, and help others do the same.
It all centers on Christ
Don't we do anything as a church? Yes, but our "doing" is not the foundation and focus; the focus and foundation is always what God is doing by His grace and power. Internal Spiritual worship and growth by the grace of God is first. Everything else we do, and there are a lot of things we seek to do as a church -- e.g., worship, fellowship, practical discipleship, service, missions, outreach, and evangelism, etc. -- flows from this. So everything else we do is secondary by definition.
"And we all, with unveiled face, beholding the glory of the Lord, are being transformed into the same image from one degree of glory to another. For this comes from the Lord who is the Spirit." (2 Corinthians 3:18).
As a pastor and preacher, my number one priority and passion -- by God's grace and mercy -- will always be ministering Jesus and His wonderful mercy, power, compassion, and grace to weak and weary sinners.
Lost sinners need to behold and be changed by the glory of God in Christ by faith so that they will be saved, finding forgiveness, hope, and the gift of eternal life on the basis of Christ's death and resurrection as they look to Him in faith.
And also, saved sinners need to behold and be changed by the glory of God in Christ by faith so that they will be strengthened, sustained, and comforted in Christ; that they will be further conformed to the image of Christ "from one degree of glory to another." In both instances, the help "comes from the Lord who is the Spirit." As David sang:
"Behold, God is my helper;
the Lord is the upholder of my life." (Psalm 54:4)
So yes, we do lots of things at church, but the main reason we come is to be helped by the Lord by looking to Jesus in faith and being ministered to by His Word and Spirit for the glory and praise of God.
A worship service is a gathering of the weak looking to God for strength, fools looking to God for wisdom, the confused looking to God guidance, the proud looking to God for humility, the tempted looking to God for victory, the depressed and lonely looking to God for comfort and compassion, sinners looking to God for grace, mercy, forgiveness, peace, joy, patience, love, hope, etc.
God does not need anything from us; but we need everything from God.
It's All for the Praise and Glory of God
We most glorify God when we look to Christ, rest in Him, and trust in Him to be conformed to His likeness. We aim for our ministries to honor and glorify God in all we do (1 Corinthians 10:31; 2 Corinthians 5:9; Colossians 3:17; 1 Peter 4:11), but all that is secondary to -- all that must be the result of -- God's ministry within us by the power of His Word and work of His Spirit in, through, and for our risen Lord and Savior, Jesus Christ. Therefore, our perpetual first order of business is to,
"But grow in the grace and knowledge of our Lord and Savior Jesus Christ. To him be the glory both now and to the day of eternity. Amen." (2 Peter 3:18)
It All Depends on God's Word and Spirit
The Bible. We know about all of the above and can strive to live it out because God has revealed Himself, His purpose, His will, and His great salvation to us in the Bible, God's holy and authoritative Word. In other words, we know how to live for God as Christians and as a church because, first, God has given us a clear, perfect, and sufficient Word to be our guide.
"All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness." (2 Timothy 3:16)
And second, because God's Spirit uses the Word to open our hearts, change our minds, and enable us to receive, grasp, love, and strive to apply it by grace through faith in Christ.
"For the word of God is living and active, sharper than any two-edged sword, piercing to the division of soul and of spirit, of joints and of marrow, and discerning the thoughts and intentions of the heart.  And no creature is hidden from his sight, but all are naked and exposed to the eyes of him to whom we must give account." (Hebrews 4:12–13)
I can promise you that no one who has truly experienced the grace and power of God's Word has ever regretted it or wanted to go back from what they've found. God's grace and power gives peace to the soul, assurance before God, perspective in life, hope for eternity, and so much more.
Those who find God can truly confess and, therefore, truly relay the invitation to others:
"This poor man cried, and the LORD heard him
and saved him out of all his troubles.
 The angel of the LORD encamps
around those who fear him, and delivers them.
 Oh, taste and see that the LORD is good!
Blessed is the man who takes refuge in him!" (Psalm 34:6–8)
Those who find peace for the soul through faith in Jesus join the song:
"I will bless the LORD at all times;
his praise shall continually be in my mouth.
 My soul makes its boast in the LORD;
let the humble hear and be glad.
 Oh, magnify the LORD with me,
and let us exalt his name together!
 I sought the LORD, and he answered me
and delivered me from all my fears." (Psalm 34:1-4)
Therefore, come hear the Word and seek, by God's grace, to humble yourself under His authority that you may experience His grace and power.
What does all this look like at the practical level?
It looks like all things centering on the preaching of Christ in the power of the Spirit from and according to Scripture. From this hub, from this centerpiece, comes Christ-centered, Spirit-filled fellowship, encouragement, singing, praying, offerings, the Lord's supper, and baptisms.
The preaching of Christ includes the heralding and exulting in the person of Christ, the work of Christ, all the blessings that result from His work, and how, by the Spirit of Christ, we come to share and enjoy those blessings by His Word and Spirit. From there, there are countless glorious implications and applications for Christian living inwardly, outwardly, and in all spheres of life.
My first and last invitation to come visit our church would be something like this, "Come and hear of God's grace in Christ." Why? Because:
"Faith comes from hearing, and hearing through the word of Christ." (Romans 10:17)
Back to Purpose
My personal purpose in life is to behold and be changed by the glory of God in Christ by faith, and help others do the same. I'm trusting God for all the effects and outward application to that, but before any of that, I need God's help -- His grace, comfort, and transformative power -- on the inside first and foremost.
My prayer for my family and friends is that they will behold and be changed by the glory of God in Christ by faith,
My prayer for the members of our church is that they will behold and be changed by the glory of God in Christ by faith,
My prayer for guests of our church is that they will behold and be changed by the glory of God in Christ by faith,
God's purpose in all things is to manifest His glory and grace through Christ, so therefore our purpose is to behold His glory and grace in Christ and, by faith and working of the Spirit, be changed by what we see for the glory, honor, and praise of God forever and ever, amen.
I will say it one more time for good measure: