What does that mean?
Those who left Heaven & took on human form produced offspring and were thrown in hell on account of it.
No, specifically, they crossbred kinds... THAT is the problem.
Angels aren't in Heaven procreating and neither will we.
How do you know? Because of one verse that you may well be misinterpreting? Why do angels have seed?
God's purpose for marriage is to procreate and since there is no marriage in Heaven, there will be no procreating in Heaven.
So plants marry? and animals marry?