Douglas F. Kelly compares God's ability to speak light into the dark human soul and make it reborn to God's speaking light into existence.

The Sending Forth of Light

The Ancient of Days (William Blake, 1794)

A third divine action occurred on the first day of creation: 'And God said, Let there be light: and there was light' (Gen 1:3).  Elsewhere in Scripture we learn that God Himself is uncreated light (e.g. John 8:12; 1 John 1:5; Revelation 21:23; 22:5).  But now the One who is light and 'swells in light inapproachable' (1 Timothy 6:16) commands forth created light into the darkness of t he yet unformed earth.

The mighty hand of God shaping and organizing the dark, watery mass in the direction of a beautiful garden

The Creation – Bible Historiale (c. 1411)

The speaking into existence of the created light is the first of a series of three separations accomplished by the Creator which were essential to make the chaos into a cosmos.  On Day One, light separates day and night; on Day Two the 'firmament' separates the upper waters from the earth, constituting an atmosphere or 'breathing space'; and on Day Three, the waters below the heavens are collected into seas, and thus separated from the dry land.  These three separations show the mighty hand of God shaping and organizing the dark, watery mass in the direction of a beautiful garden; a fit and lovely swelling place for plants, animals, and humankind.

The Genesis Flood: The Biblical Record and its Scientific Implications is a 1961 book by young Earth creationists John C. Whitcomb and Henry M. Morris that, according to Ronald Numbers, elevated young Earth creationism "to a position of fundamentalist orthodoxy."

Henry Morris would seem to be right in suggesting that with the coming of the light on the first day, '... there was established a cyclical succession of days and nights -- periods of light and periods of darkness.' He adds:

'Such a cyclical light-dark arrangement clearly means that the earth was now rotating on its axis and that there was a source of light on one side of the earth corresponding to the sun, even though the sun was not yet made' (Genesis 1:16).  [Since] '... the presence of visible light waves necessarily involves the entire electromagnetic spectrum … setting the electromagnetic forces into operation completed the energizing of the physical cosmos ...'

The biblical view of reality never separates God

from the elements He created and controls

Depiction of Genesis 1:2 by Wenceslaus Hollar

The question of how there was light on earth before the sun was created (on Day Four -- Genesis 1:14) brings us back to the biblical view of reality, which never separates in deistic fashion God from the elements He created and controls.  We are simply not told what the source of light was before the sun was placed in the sky.  All the text says is that God spoke and the light was there.

Reality is untrammeled by man-centered assumptions

which would bring God down to our finite level

Creation of Light, by Gustave Doré

John Calvin's admonition should be taken to heart if we wish to grasp reality as it is, untrammeled by man-centered assumptions which would bring God down to our finite level:

Therefore the Lord by the very order of the creation, bears witness that he holds in his hand the light, which he is able to impart to us without the sun and moon.

Should this be thought difficult for One who is light?

The first time God speaks in Scripture, light appears and a person whose life is darkened and condemned by sin, becomes 'light in the Lord'

The Conversion of Saul on the road to Damascus as painted by Michelangelo

It is significant that the first time God speaks in Scripture, light appears.  According to Psalm 119:130, 'The entrance of they words giveth light'.  It was so in the old, original creation, and the apostle Paul tells us that something similar happens in 'the new creation', when a person whose life is darkened and condemned by sin, becomes 'light in the Lord' (Ephesians 5:8).  In 2 Corinthians 4:6, he quotes directly from Genesis 1:3: '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.'  Such an enlightening of the human personality as it is enabled to see who the Son of God really is, constitutes nothing less than 'a new creation' (2 Corinthians 5:17).

Only someone so great as the mighty Creator God could speak light into the darkness of the primeval earth and able to speak light into the dark human soul making the chaos of sin into the cosmos of a new creation in Christ

Separation of light and darkness on the first day of creation, from the Sistine Chapel ceiling by Michelangelo

The analogy between the two creations is fascinating.  Only someone so great as the mighty Creator God could speak light into the darkness of the primeval earth in the first creation.  Only He -- the Almighty Word, the uncreated Light -- is able to speak light into the dark human soul of the smallest child or greatest king, and thus bring it into a new birth (see John chapter three and Jeremiah chapter thirty-one), making the chaos of sin into the cosmos of a new creation in Christ.  And in both cases, the instrument of transforming enlightenment is His spoke word, which never 'returns to him void' (Isaiah 55:11).  His 'fiat' command (as the Latin translation of the Bible phrases 'let there be') always finds fulfillment.  Whenever God commands light into the dark, formless elements of earth or into the spiritually blind energies of self-defeating human psychology, light appears in both scenes and beauty replaces disorder.

Source: Kelly, Douglas F.  Creation and Change -- Genesis 1.1 - 2.4 in the Light of Changing Scientific Paradigms.  Scotland, U.K.: Christian Focus Publications, 2017, pages 108-110.