What translation are you reading?
The "engagement period" for Jews back then was considered a covenant.
Look at Joseph and Mary.
They were engaged when she was found with child.
When Joseph found out she was pregnant, he was contemplating divorce.
Matthew 1:19
Because Joseph her husband was faithful to the law, and yet did not want to expose her
to public disgrace, he had in mind to divorce her quietly."
In today's world?
Divorce can only take place after a marriage had been completed.
But, when Jews were under an engagement "covenant?"
The Jewish man and woman were considered good as married, though not yet man and wife.
And, that is what the Church is today!
We are under the new covenant with Christ. Guaranteed to be married!
The marriage will actually be consummated when we are resurrected!
We will have become "one flesh."
Genesis 2:23-24
The man said,
“This is now bone of my bones
and flesh of my flesh;
she shall be called ‘woman,’
for she was taken out of man.”
That is why a man leaves his father and mother and is
united to his wife, and they become one flesh.
When we are finally resurrected! We will have become "one Flesh!:"
In the mean while?
We are to be receiving benefits according to the new covenant.
Jews were promised there would be a day when this new covenant will come to pass.
Those benefits are what the maturing in Christ will realize now in time.
But, for this new covenant? Gentiles who now believe, have been grafted into those same benefits!
grace and peace .........................