V.15-17 The unloved wife is a picture of Israel, the one God first chose. Because of their sin, in crucifying Jesus, they had to be put away — Israel today. So God turned to us, the Gentiles (the wife beloved); the heavenly and only bride of Christ (Acts 28:26-28). Nevertheless, after the believers are caught away to heaven, God will once again take up His earthly people. As it were, the child of the apparently rejected one, shall be the one to receive the inheritance on earth.
V.18-21 A picture of Israel, as a nation, which has been a rebellious child of God. They shall be the ones punished and destroyed at the end of the tribulation (vvs. 19-21).
V.22-23 Christ was hanged on a tree (1 Pet. 2:24). He was made a curse for us (Gal. 3:13).