A somewhat literary or formal term for the promises exchanged in marriage; often used in poetic or ceremonial contexts.
The two exchanged marriage vows at the church.
A more common and neutral term for marriage vows; 二世の約束 carries a slightly more poetic or old-fashioned nuance.
Compound of 二世 (にせ, 'two worlds' or 'this and the next life') and 約束 (やくそく, 'promise'), suggesting a vow that extends beyond this life.