We are currently apart of the new covenant.
The new covenant reaches further fulfillment on Jesus' return - then "the knowledge of the Lord will be as the waters cover the sea." We will not reach this point until the gospel has spread to all nations:
And this gospel of the kingdom shall be preached in all the world for
a witness unto all nations; and then shall the end come.
Currently, we are in a transition phase as we await the fulfillment of Ezekiel 37-38 and other end times prophecies.
They have moved me to jealousy with that which is not God; they have
provoked me to anger with their vanities: and I will move them to
jealousy with those which are not a people; I will provoke them to
anger with a foolish nation.
20-21 -I stand in doubt of you. Tell me, ye that desire to be under
the law, do ye not hear the law?
22 For it is written, that Abraham had two sons, the one by a
bondmaid, the other by a freewoman. 23-24 BUT HE WHO WAS OF THE
BONDWOMAN WAS BORN AFTER THE FLESH; but he of the freewoman was by
promise. Which things are an allegory (allégoreó): for these are the 2
covenants; the one from the mount Sinai, which gendereth to bondage,
which is Agar.
25 For this Agar is mount Sinai in Arabia, and answereth to Jerusalem
which now is, and is in bondage with her children.
26 But Jerusalem which is above is free, which is the mother of us
27 For it is written, Rejoice, thou barren that bearest not; break
forth and cry, thou that travailest not: for the desolate hath many
more children than she which hath an husband.
28 Now we, brethren, as Isaac was, are the children of promise.
29 But as then he that was born after the flesh persecuted him that
was born after the Spirit, even so it is now. Nevertheless what say
the scripture? 30 Cast out the bondwoman and her son: FOR THE SON of
the bondwoman shall not be heir with the son of the freewoman.
31 So then, brethren, we are not children of the bondwoman, but of the
V28-29: Notice there were already those born after the spirit in Abraham’s time.
- (Bondswoman) Agar is figuratively likened to the Old Covenant (Mount
Sinai) and represents individuals of her whom are bound to sin and
born by the flesh.
- (Freewoman) Sarah is figuratively likened to the New Covenant (New
Jerusalem) and represents individuals of her whom are free from sin
and born by the spirit.
In Genesis, God promised Abraham a son through his wife Sarai (Sarah) whom was infertile (Ge. 15:2-4, 16:1-2, 18:12-15). This son was Isaac, who was born because of a divine promise from God and God made his covenant with him (Ge. 17:15-21) and the 12 tribe tribes of Israel descended from him. Abraham and Sarah decided for Abraham to have another son with his other wife who was a bondwoman (Ge. 16:15). This son he had by Agar was Ishmael, who did not come about due to a divine promise but a natural fleshly way. Ishmael also mocked Isaac, and was cast out of Abraham’s house which God approved of (Ge. 21:8-12).
It should be made clear that the meaning of this story is at the forefront: that God will toss out the bondwoman’s son (those born after the flesh: v23, 30). Ultimately, this allegory boils down to being a child of promise accepted by God for New Jerusalem, while the story’s persons, then these person’s traits which are assigned to the covenants are used together to illustrate this hidden lesson. This is not about God’s promises made to the national body of Israel (Ro. 9:3-4), and the assigned traits are not all inclusive for every individual. David, Moses and the other prophets from the Old Covenant will still be ‘children of the free women,’ (Lu. 13:28-29) and so will Abraham because he had faith in God’s word despite not being under either covenant. This allegory seems to have been given as a warning to those Galatians seen in the previous chapter (Gal. 3:1-5) who had gone back to walking by the flesh (being under the law of sin).
Messianic Passages: [A]
Passages regarding Israel, the prophetic timeline, and the covenants:  
Source: Self - Messianic Jew: 1,000+ hours of Bible study.