...yet the majority (if not all) of the modern english translations do not say this. Why is that? Also, you have not touched on how one can pass from spiritual death to spiritual life apart from Christ who is referred to as The Life.
The Bible makes a distinction between the written or the spoken word of God by men and the Incarnate "Word" of God that is the "Amen" when He speaks. However, the written or spoken word does not produce what is written or spoken. The Bible makes a distinction between written revelation when read or spoken and received by the natural mind and revelation supernaturally conveyed by the Incarnate Word Himself.
When God Himself speaks the Word within a man something is CREATED within that person that was not previously there before:
For God, who commanded the light to shine out of darkness, hath shined in our hearts, to give the light of the knowledge of the glory of God in the face of Jesus Christ.
The words "For God, who commanded the light to shine out of darkness" takes the reader back to Genesis 1:2-3:
darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.
3 ¶ And God said, Let there be light: and there was light.
These were not mere spoken words but words infused by the CREATIVE POWER of God so that what was spoken was also EFFECTUAL in bringing to pass what was said. If you doubt that then you speak the same words in a dark room and see if anything happens. That is the difference between speaking in "word only" and speaking in "power...and in the Spirit".
Likewise, it is when God Himself as the Incarnate Word, the Amen speaks the gospel inside the darkened state of the sinner that His word comes in power...and in the Holy Spirit rather than "in word only" (1 Thes. 1:4-5) that supernatural LIGHT/LIFE is created revealed man and is EFFECTUAL in bringing that person to a saving KNOWLEDGE of Christ.
Notice in Ephesians 4:18 that spiritual death is defined as being ALIENATED FROM THE LIFE OF GOD THROUGH IGNORANCE THAT IS IN THEM. When God infuses the gospel words with POWER what is effectually CREATED in them is the saving knowledge of Jesus Christ. This is the effectual call of the gospel (2 Thes. 2:13-14; I Cor. 1:26-31; Rom. 8:28-32; etc.). This is being quickened (Eph. 2:1,5) and is "the workmanship of God CREATED in Christ Jesus" (Eph. 2:10).
This is giving a NEW HEART which is inherently a BELIEVING HEART when it is given. It does not become a believing heart but IS a believing heart that God gives. Therefore when God CREATES light/life/knowlege (Jn. 17:3) within the darkened/ignorant lost man He is one and the same time creating faith in Christ. There is no such person as an unregenerated believer in Christ or a regenerated unbeliever in Christ as divine quickening is producing the LIGHT/LIFE/KNOWELGE of saving faith in the sinner by God where previous that person was ALIENATED FROM THE LIFE OF GOD THROUGH IGNORANCE THAT IS IN THEM (Eph. 4:18).