19 Now we know that whatever the law says, it says to those who are under the law, so that every mouth may be silenced and the whole world held accountable to God.

Read Romans 3:19 Using Other Translations

Now we know that what things soever the law saith, it saith to them who are under the law: that every mouth may be stopped, and all the world may become guilty before God.
Now we know that whatever the law says it speaks to those who are under the law, so that every mouth may be stopped, and the whole world may be held accountable to God.
Obviously, the law applies to those to whom it was given, for its purpose is to keep people from having excuses, and to show that the entire world is guilty before God.