Charles Ellicott Commentary Isaiah 54:4

"Fear not; for thou shalt not be ashamed: neither be thou confounded; for thou shalt not be put to shame: for thou shalt forget the shame of thy youth; and the reproach of thy widowhood shalt thou remember no more." — Isaiah 54:4 (ASV)

You shall forget. —The shame of your youth, was the Egyptian bondage, from which Jehovah chose Israel to be His bride (Jeremiah 3:1–11; Ezekiel 16:1–14). The reproach of your widowhood was the captivity in Babylon.