This answer follows the Nicene Creed of 381 C.E. as its primary foundation because the Nicene Creed itself is rooted in the Scriptures.
Father = unbegotten
The Father is unbegotten because he has no source or origin of existence. No one begets the Father. He alone does the begetting. This is why he is the first person in the Trinity for he has no source but is the source of the other two persons. He is the first-among-equals ( Matthew 28:19) because he has the personal properties (function not essence) that is high than the other two, namely, (i) source, (ii) authority, (iii) primary subsistence.
The Father is the source of the other two persons. Without him,both the Son ( John 6:57, 1 John 1:1-3) and the Spirit could not exist ( Matthew 10:20).
The Father has authority over the other two persons. He alone has authority over himself, the Son (Acts 1:7, Matthew 28:18) and the Spirit. [The Son has authority over the Spirit ( John 16:13-15) but not over himself ( John 5:19) and the Father ( John 5:30)].
3) Primary Subsistence
The Son is the Wisdom of the Father ( 1 Corinthians 1:24-25) and the Holy Spirit is the Spirit of the Father ( Acts 5:3-4) and the Son( Galatians 4:6). This shows that although the three are fellow persons, only the Father is in full function of being a person not in essence (being) but in personal property ( function) that is why he is the primary or the principal subsistence. This same reason why he holds the appelation "God" ( Hebrew: El/ohim Greek: ho theos/ theos) as his distinguishing title ( 1 Corinthians 8:6).
The Son is begotten because he has source or origin of existence.
The difference between divine and human begetting:
Corporeal begetting ( Human)
Maturation age ( fertile couple at least at the onset of puberty)
Female wife is needed
Sex is needed
Offspring has beginning of existence
Spiritual begetting ( divine)
At the first instance of existence, God begets, that is, because God is eternal he begets eternally ( John 5:26)
Begetting doesn’t involve a female wife ( John 4:24, Psalm 45:1LXX)
Begetting doesn’t involve sex ( John 4:24, Psalm 110:3 LXX)
Offspring has no beginning of existence ( John 1:1, 1 John 1:1-3)
How is the Son begotten?
To beget is to produce an offspring of same essence.
In humans, sexual activity is the main mechanism of producing an offspring of same essence.
In God, there is no sexual activity needed because he is spirit ( John 4:24) but only love which itself a vital part of sexual activity in humans to beget.
LOVE and ACTION
By being love itself in his very being( 1 John 4:9), God produces his offspring. He produces him through being love. Love is in the mind. In God’s mind is his Logos. This Logos is without beginning or ending because God is coeval with his own reason, intellect and word and with his own internal activities (ad intra) as opposed to his activities though his offspring (ad extra).
*Premise 1: God produces Logos
Premise 2: Logos is eternal
Conclusion: God eternally produces Logos*
Hence, in mathematical formula, God’s begetting is like this:
Love + thinking – Sex = Offspring
My heart emitted my most excellent Logos (Psalm 45:1 LXX)
I birthed you from my womb before the morning star (Psalm 110:3 LXX)
TIME and ETERNITY
Every activity or acts of God has time in it. God makes his own time by acting. Action demands time. Or to put it more clearly:
Action is something that is done. "Done" means it was completed in the past. When you do something, "do" is in the present tense. Both past and present tense is in relation to time. Therefore, action demands time.
Time doesn't have to mean change. You could walk out of a room and five minutes later come back to the exact same room.
The time of the begetting can be explained as coevality with God because he is the begetter:
Proverbs 8:25 LXX
He begets me (active voice)
I am begotten by him ( passive voice)
Begets (Present Tense) Am ( present tense) , Begotten (Past
This highly presupposes the being of God is the point. God is without beginning or ending. He is who he is. He simply is. He is the I am who I am. The Greek says “ I am the (sole) one existing (eternally)” capturing the Hebrew’s denotation per se.
*Premise 1: Begetting in the present time (Proverbs 8:25 LXX)
Premise 2: God is the one who begets
Premise 3: God is without beginning or ending (Exodus 3:14)
Conclusion: The present time reflects back to eternity for God is the begetter himself.*
Admittedly, the question of how is the Son begotten? is a very tough question to answer because we humans are trying to grasp the infinite but this doesn't mean we can't know the answer. In fact, it was given already by God himself through revelation in the Holy Scriptures.
The Son has no beginning of existence because of three reasons, namely, (i) consubstantiality,(ii) spirituality,(iii) internal relations (personal property)
"Like begets Like."
A Father that has no beginning has a Son that has no beginning.
A Father that has a beginning has a Son that has a beginning.
The former is divine reality while the latter is a fleshy reality,of human nature. Both realities corresponds to the scientific law of biogenesis and Gregor Mendel's laws in Genetics.
The origin or source of the Son is the Father.
Naturally and inevitably the Son is caused to exist.
The difference between the begetting of Jesus and of the saints:
The begetting of the Christian
John 1:12-13, 3:3-7, 1 Peter 1:3- Christian begotten again by God himself and is born again
2 Peter 1:4 -Christians participates in God's own nature.
Romans 8:15- Christians are adopted children of God
Galatians 3:26 -children of God through faith
The begetting of the Son
Proverbs 8:22-30 compare to 1 Corinthians 1:24-25, (Compare Romans 1:3-4 to Acts 13:35, Hebrews 1:5, 5:5), 1 John 5:18 -The Son begotten by the Father himself.
John 1:1, Philippians 2:6, Colossians 2:9 - The Son has God’s own nature.
John 5:18, Romans 8:3 – The Son is God’s own i.e. proper Son
Hebrews 1:2-3 -- The Son of God through communication of nature
The begetting is not physical but metaphysical. It happens in the being of God as spirit ( John 4:24).
The Father has one nature. This nature is indivisible. Because of this, either the Son has the whole nature or not. He can't be part of the whole for God's nature is indivisible. Ergo, the Son has the whole substance of the Father. He was not from nothing ( ex nihilo) but from the Father ( John 16:28).
3. Internal relations ( personal property)
The Son is the reason, wisdom and power per se of the Father.
The Offspring of God is his very own: (i) logos (John 1:1) (ii) sophia ( Hebrews 1:3) (iii) dynamis ( 1 Corinthians 1:24)
In the begetting of the Son, there is a real originination of existence and there is a real production that is happening not just a metaphor.
The Son truly has an origin or source of his very existence. He is not dependent of himself for existence because he himself is a son. He depends on his Father for existence.
" The Son is auto-theos because of his nature not because of his sonship."
The Son has an origin of existence (i.e. the Father) but does not have a beginning of existence.
Someone/something who has an origin can still be co-eval with its source.
A heavy ball is placed on a cushion, there's a depression caused in the cushion. The moment it was placed on the cushion was the exact moment when the depression was caused. Hence, the cause and the effect are coeval.
In the Bible, the Father begets the Son. The cause of the Son is the Father but yet he is without beginning because the Father is without beginning.
The Scriptures itself in John 1:1-3 and 1 John 1:1-3 stated that the Son, the Logos, is "from the beginning( i.e. God)" for God is the " beginning, origin and source of all things" ( 1 Cor. 8:6).
God truly produces his offspring.
The Father ( the Primary Subsistence) begets ( produces) his own Son ( Wisdom, Power, Word) out of his own self.
How do the Father begets his own Son out of himself?
Through t*hinking of his own self*.
Thinking- a process of intellect by which a rational being knows and understands and makes actions and judgments.
When we think, we use our schema (i.e. past information) to either form a new one from it or to add a new one from it.
Information is gained via experience and hence the term "experiential knowledge".
But in God, he has the ability to know all things but he doesn't have ability to experience all that he knows for he has the trait of immutability, that is, he cannot do anything that contradicts his nature.
God knows hell but he cannot experience it.
A human person thinks of himself, gaining self-knowledge. A man is a duality of expressive image. He is both corporeal and spiritual. The flesh is the body while the psyche is the mind/spirit. The psyche is responsible for gaining the ultimate meaning of the whole personality while the body is through which personal function is experienced via the senses.
The fact is, humans do not have complete, perfect knowledge of himself. This case is evident in the first instance of human existence, and what is that single word that describes the whole of happenings in a human being? GROWTH and or DEVELOPMENT. Hence, showing our incompleteness per se in our very own being.
In God, however, neither is growth nor development needed for he is complete in himself.
The evidence that God is perfect is as follows:
(i) logos- God does not need an explanation, logic and understand of anything existing including his own existence from outside himself ( ad intra) . We humans, being rational, does make reason and do reasoning involving logic and understanding form outside ourselves ( ad extra).
(ii) sophia - God doesn't need knowledge to make wise decisions on a matter. We humans need knowledge and specifically, an experiential knowledge to make right judgments, decisions etc.
(iii) dynamis - God doesn't need food, water, etc. to have the ability to do something. We humans, without proper nourishment, will inevitably be in the state of malfunction , inertia and eventually,of demise.
Why God doesn't need human operations for his divine traits?
It is because he is not human! His own logos, sophia and dynamis are in fact, the very function of his own Son.
In the generation of the Son out of the Father through self-thinking. This is like seeing your self in a mirror that reflects all of your totality: body, soul and spirit, with all of its minute details. In God, however, he is perfect. His own being generates a second person of himself. A Person -- not nature-- produces another person. In this act we have the following:
(1) Distribution of substance(2) Distinction of persons
(1) Division of substance