Albert Barnes Commentary Romans 7:3

"So then if, while the husband liveth, she be joined to another man, she shall be called an adulteress: but if the husband die, she is free from the law, so that she is no adulteress, though she be joined to another man." — Romans 7:3 (ASV)

So then if, etc. Compare to Matthew 5:32.

She shall be called. She will be. The word used here (crhmatisei) is often used to denote being called by an oracle, or by Divine revelation. But it is here employed in the simple sense of being commonly called, or of being so regarded.