The Deity of Christ may be proved from the divine perfections He possesses - "for in him dwells all the fullness of the Godhead" (Col. 2:9) - not one perfection of the divine nature excepted. Otherwise it could not be said that all the fullness of Deity was in him. God is necessarily self-existent and independent of any. So it is with Christ - he is autoyeov, God of himself. As man and mediator, he has a life given him for himself and others, and lives by the Father. But, as God, he owes his life and being to none - it is not derived from another; he is over all, God blessed for ever.
Eternity is a perfection of God. God is from everlasting to everlasting. Christ was not only before Abraham, but before Adam, and before any creature was in being, for he is the beginning, the first Cause of the creation of God, (Rev. 3:14) the first born, or rather, the first parent and producer of every creature; as the word prwtotokov, by the removal of the accent, may be rendered, which best agrees with the apostle's reasoning in the next verse where all things are said to be created by him. Therefore, as the apostle Paul argues, he must be before all things (Col. 1:15-17).
He was set up from everlasting; his goings forth in the covenant were of old; the elect were chosen in him before the foundation of the world; and had grace given them in him, before that began - all of which suppose his eternal existence. For this reason, he is called Alpha and Omega the first and the last, the beginning and the ending; which is, and was, and is to come; a type of Melchizedek, having neither beginning of days nor end of life (Rev. 1:8; Heb. 7:3).
Omnipresence is another perfection of Deity (Jer. 23:23, 24). Christ, as the Son of God, was in heaven, in the bosom of his Father, and, at the same time as the Son of man, he was here on earth (John 1:18, 3:13), which he could not be if he was not omnipresent. He also could not make good his promises to his ministers, churches, and people to be with them at all times, in all ages, and in all places, wherever they are (Matthew 18:20, 28:20).
Adapted from A Body of Doctrinal Divinity, Book 1, Chapter 30, by John Gill.