In general, mothers in the Bible represent the Lord's church on earth, or the church among those who know and follow the Lord. In some cases "mother" more specifically means the truth of the church, the true teachings the church has about the Lord and about life.
This makes sense if you think about it. Mothers are the vehicles through which new people are created; the church (in a broad sense) is the vehicle through which new ideas about the Lord and new good actions are created. And just as a mother is filled with love – for her children and, ideally, for her husband – so also is the church filled with love, both for its ideas and uses and also for the Lord.