How is Christ the Head of the Church?

The Church is composed of all Christ’s true disciples. The Church is one holy catholic [meaning: global]
body, founded upon the apostolic teaching as found in Scripture. According to Christ’s commandment, Christians are to associate themselves into particular congregations or churches. I believe that the Lord Jesus is the only Head of the Church, and in Him is invested supremely all power for its government.

If Jesus is the only Head of the Church, and if Jesus is currently seated at God the Father's right hand until His enemies are made a footstool, and we cannot see Him face-to-face until His second coming, then how does Christ exercise His headship–His authority–over the Church?

As Head of the Church, Jesus–whom we do not currently see face-to-face–exercises His authority over His people through the apostles He appointed. Though we can't see the apostles face-to-face either, we have access to the apostles’ teaching through the Holy Spirit-inspired New Testament writings. NOTE: 

• New Testament writings must have a place of prominence in considering the headship of Christ over the Church.
• This is NOT to denigrate the Old Testament. Through the words of Christ our Lord and His apostles, we know that the Old Testament scriptures are equally inspired with the New Testament. ALL Scripture is the very Word of God transmitted by Him in a verbal, plenary manner (Matt 5:18) and is as truthful and authoritative as God Himself (John 17:17). Its authority is derived from its Author and not from the opinions of men (2 Pet 1:20-21). All Scripture was given by inspiration of God, is infallible and inerrant, and is the sufficient, final arbiter of all disputes concerning matters of life and godliness (2 Tim 3:16-17).
• The New Testament scriptures, however, are especially instructive to the Church, as they illuminate how we are to live in the current New Covenant era, which was inaugurated through the historical, earthly ministry of Christ. (“Testament” means “covenant,” so the New Testament scriptures are those applied to the New Covenant community.)

Through the New Testament scriptures, inspired by the Holy Spirit, and written down by the apostles (or by their close associates), Christ exercises authority over His Church by establishing points of doctrine, the pattern of church government, principles of gathered worship, and procedures for church discipline to be followed in the local congregations. 

Points of Doctrine

The first way in which Christ exercises authority over His Church is by establishing points of doctrine; that is, Christ gives us specific teachings, which we must confess and believe. Christ is the Word of God from the beginning (being God Himself and with God, John 1:1), and so we look to the entire canon of Scripture for our doctrine. However, Christ is specifically exalted as Head over the Church in the new covenant era, and we see certain teachings—about the trinity, for example, or the nature of the afterlife—come into much clearer focus following the historical work of Christ. Right doctrine allows us to know Christ better, to glorify Him for who He is, and to tell others about Him with confidence. Right doctrine leads to greater harmony among believers, as the unity of the church congregation must be grounded in doctrinal agreement.

Pattern of Church Government

The second way in which Christ exercises authority over His Church is by establishing the pattern of church government. The regular officers of a Church are of two kinds: [1.] Bishops, Pastors, or Elders (as appointed by other Bishops, Pastors, or Elders and agreed upon by the congregation) and [2.] Deacons (as elected by the congregation). SEE: Acts 20:17, 28; Phil. 1:1; Titus 1:5. 

In The Loveliest Place, Dustin Benge notes:

[Christ heads His Church] through the instrumentality of godly leaders (1 Thess. 5:12-13; Heb. 13:7, 17). Pastors, elders, and deacons are representatives of Christ's authority over the church. Paul summarizes the purpose of these shepherds this way: "to equip the saints for the work of ministry, for building up the body of Christ" (Eph. 4:11-12)... authority the leaders of the church possess is a delegated authority from Christ. It is always Christ, and Christ alone, who governs the church. The sole responsibility of those given charge in leading, teaching, preaching, and serving her is to declare and apply the instructions of Christ as revealed in his written word.

By establishing the pattern of church government, and tying the authority of church government directly to the Bible–hemming in officers, so that they do not go beyond God's Word–Christ exercises His own authority over His Church.

Principles of Gathered Worship

The third way in which Christ exercises authority over His Church is by establishing principles of gathered worship. 

As the elders of Grace Heritage Church have noted:

Worship is the corporate expression of the delight, awe, and thankfulness that come from knowing our infinitely glorious and sovereign God and Savior. Because the distance between God and His creatures is so great, the only acceptable way of approaching God in worship must be revealed to us by God Himself. Therefore, He may not be worshiped in ways invented by us. This principle protects us from idolatrous worship and focuses our energies on those activities through which God has called us to draw near.

Congregational worship of God is composed of: the reading of the Scriptures; preaching, and hearing the Word of God; teaching and admonishing one another in psalms, hymns, and spiritual songs, singing with grace in our hearts to the Lord; prayer; the giving of tithes and offerings; greetings and announcements; as also the administration of baptism, and the Lord's Supper. These are to be performed in obedience to him, with understanding, faithfulness, and affection. Moreover, solemn humiliation with fastings, vows, and thanksgivings upon special occasions ought to be used in an holy and religious manner.

Procedures for Church Discipline

The fourth way in which Christ exercises authority over His Church is by establishing procedures for church discipline. Church discipline is to be conducted according to the commands of Christ recorded in Matthew 18:15-17 and the commands of the Apostle written in passages such as 1 Corinthians 5:1-13, 2 Thessalonians 3:6-15, 1 Timothy 5:19-20, and Titus 3:10-11. Church discipline shows the Church's submission to Christ and demonstrates the seriousness with which the Church views Christ's call to follow Him in holiness.

Conclusion

Practically speaking, how is Christ the Head of the Church on a week-to-week basis? Christ exercises His headship over local congregations in four ways: by establishing points of doctrine, the pattern of church government, principles of gathered worship, and procedures for church discipline to be followed in the local congregations. By recognizing Christ's headship, and by seeking to discern specifics of His headship through looking intently into His Word, the Church is empowered in:

1. living harmoniously (members seeking Christ's will rather than their own preferences)

2. enjoying and glorifying Christ for who He is and what He has done for us