Two questions of the Belgic Confession

I'll confess to not fully understanding the question, but:

"filling heaven and earth" is intended to convey that we are speaking of the divine nature which, as such, is omnipresent and upholds all things and sustains their being. This corresponds to, and is contrasted with, his human nature, which, it says, rightly, "has a beginning of days" (proven if by nothing else that He was "he who came, as to the flesh, of the seed of David" Romans 1:3).

The Son of God who "upholds all things by his powerful word," (Hebrews 1:3) and "is before all things and in whom all things hold together," (Colossians 1:17) and "through whom all things without exception were made" (John 1:3) was not, as to his person, dignity, etc. created. It is the human nature with which the Father furnished Him, by the Holy Spirit, of the virgin Mary (Galatians 4:4; Luke 1:35).

I couldn't make out what was being said about 'He vs. the male baby,' but there seems to be some confusion about something relatively simple.

In this confession of faith, restating prior Councils of the Church, is stating the position that in Christ Jesus there is but one person, to whom is proper, since the incarnation, two natures.

This is summed up in the prologue of John's Gospel (1:1, 14), where we read:

In the beginning was the Word, and the Word was with God: and the Word was God. ... And the Word was made flesh and made his dwelling among us.

There is one person in view here, the Word, or Son (v. 14), of God, and two natures: the divine, which makes Him a divine, not merely human person, and the human nature which He takes on for our salvation. It's one divine person with a divine nature and a human nature. Not a divine person and a human person.

What you described seems dangerously close to Nestorianism, a heresy which creates a distinction between the divine and human nature which is not warranted, that is, to the point of actually creating two persons in Christ: the 'divine Jesus' and the 'human Jesus.'

What one says of the properties of Christ's human nature you say of Him, the one person: a divine person to whom said human nature belongs. What you say of the properties of Christ's divine nature, youalso say of Him—the very same person.

Hence we read in Scripture things like (Revelation 1:17-18):

And when I saw him, I fell at his feet as though dead. And he placed his hand on me and said: Fear not, I am the First and the Last, even he that lives: and I became dead, but behold I live forever and I have the keys of Death and the realm thereof.

It was "the First and the Last" who died because He took on a nature in which it is possible to be killed (be separated in spirit from your body). Here one nature died, one didn't.

Similarly (1 Corinthians 2:8):

[The mysterious and hidden wisdom of God] none of the rulers of this age knew: for had they known it, they would not have crucified the Lord of Glory.

And again (Acts 3:14-15; cf. John 14:6):

But you rejected the Holy and Just One, and asked that a murderer of a man to be realeased to you instead as a favor:¹ you killed the Author of Life, whom God raised from the dead: of which we are witnesses.

So when you speak of Jesus, you are speaking of one and the same Lord, Son, Word, God, with two natures equally His own. The divine from all eternity; the human since the Incarnation. Not change to His divine nature which never changes and more than the rest of creation changes His divine nature.

Matthew 1:21-22 And she shall give birth a son: and you shall give him the name Jesus: for he shall save his people from their sins. Now all this was done that it might be fulfilled which the Lord spoke by the prophet, saying: Behold a virgin shall concieve and give birth a son, and they shall give him the name Emmanuel, which translated means, God with us.

Cf. John 1:1, 14.

Luke 1:43 And why has this been granted to me, that the mother of my Lord should come to me?

Cf. Isaiah 9:6 et seq.

^{1 Cf. Jn 18:39}