Mother (Maa), is such a word which consists the whole world. Everything which is necessary for life is given by mother. We say this earth Dharti Maa because she gives us place to live. Grains used for food is given by Anna(purna) Maa.
Without food we can’t live longer and starve to death. All the things which are necessary for life is given by different natural mothers. But our mother, which has given birth to us is a whole world in herself because she give us place in her lap like Dharti Maa and feed us her own milk to satiate our hunger like Annapurna Maa. The god given us the boon in the form of mother (Janani). Mother is one who understands our every needs and fulfills them in time. He who understands the meaning of this word makes his life delightful.
The word devi used for woman who is above all, superpower, care taker and the creator and director of the whole universe. That woman who gives us birth, we call her mother because she is it self an universe and one who gives birth and creates the whole universe is called Devi Maa.