25 ¶ Now concerning virgins: I have no commandment from the Lord; yet I give judgment as one whom the Lord in His mercy has made trustworthy.

In the context of the church at Corinth, and the ongoing persecution the virgins were advised not to marry if possible. Marriage will add to their burdens. If anyone decided to stay single or marry it was  personal and did not amount to any sin whatsoever either way, if voluntary. Married life has more troubles than single state. It exposes one to more cares and wants.