as Sarah obeyed Abraham, calling him lord, whose children you now are, if you do well, and are not put in fear by any terror.

 She must be submissive. It is not a spineless submission that is meant but, as someone has finely put it, a "voluntary selflessness." it is the submission which is based on the death of pride and the desire to serve. It is the submission not of fear but of perfect love. 