Merriam Webster defines preeminence as:  having paramount rank, dignity or importance. 

We can say then, that Christ is to be placed first in all.  And that is exactly the meaning in Col 1:18 above - He is from the beginning (first), firstborn from the dead (first), head of the body/church (first). 

The Old Testament was all about Jesus Christ, for Jesus said in John 5:39  "Search the scriptures; for in them ye think ye have eternal life: and they are they which testify of me."  The New Testament is about Christ: His birth, His life, His death and His resurrection. We have heard it said that the Old Testament is the New Testament concealed, and the New Testament is the Old Testament revealed. 

Christ was the central theme of the apostle's preaching and writing. Paul in the book of Colossians focuses the reader's attention on Christ's preeminence.

God's Holy Word says that Christ is preeminent in our salvation. (Co. 1:13-14; Eph. 1:7.) Without Christ you cannot be saved. No one but Him has died for the sins of all mankind and in no other can the way to heaven be found.  The Catholics teach that Mary is their Mediatrix, that it is through her intercession alone can man find salvation.  They teach that it is through her pleadings that one will be saved.  This is in direct opposition to John 14:6  "Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me."  The Bible nowhere says that Mary will plead to Jesus, and then Jesus will pray to the Father.  Only Jesus shed His blood for us, and that is what entitles Him to be our redeemer.  To say otherwise is to take away the power of what was done at the cross.

Christ is preeminent in creation (Col. 1:16-17, Heb. 1:1-2.) Not only does Christ have the right to expect obedience from us because of Him dying for us, He has that right as our Creator.

Christ is preeminent in the church (Col. 1:18; Eph. 1: 22-23.) If your congregation is not Christ-centered, if Christ is not the guiding light of your work then you are looking toward the wrong head. No one can replace the authority of Christ here on earth. Just as he is preeminent in the church, He is preeminent in the preaching and teaching that is conducted there. (Col. 1:28; 1 Cor. 2:1-2.)

Jesus does not share His Headship with anyone on earth.  There is no need to.  He does not need an invisible head to lead the body.  He left us with His words, and when we follow those words, we follow Him.  2 John 1:9  "Whosoever transgresseth, and abideth not in the doctrine of Christ, hath not God. He that abideth in the doctrine of Christ, he hath both the Father and the Son."  Which "head" is your doctrine coming from?  If it is different that what the Holy Spirit revealed in the written word, then it is not from heaven, but from man.

Also, when Christ is not taught and socializing or entertainment becomes the focus then He is no longer preeminent in our worship and service (Col. 3:16-17.) This is one thing that makes our worship vain (empty) [Matt. 15:9] and useless. Man's way cannot replace the preeminent Christ in the church.  Unfortunately, many churches of Christ are going the way of denominationalism in this regard.  They think that instrumental music, plays, dramas, coffee and doughnuts, gymnasiums, soft sermons, etc. are necessary to appeal to the masses.  The truth of the matter is, if they come for those reasons, they'll also only stay for those reasons.  The Word of God is the only appeal necessary for those who are interested in spiritual things. 

Christ is preeminent in our lives (Col. 3:4; John 14:6.) We cannot lose our way if Christ is first and foremost in our lives. He must direct us in all that we do or else we will find ourselves wanting on the Day of Judgment.