The starter, after being frozen, needs to come back up to room temperature to begin it's work. Yeast is a living organism, and requires moisture, temperature, and food. Also, adding just a bit of diastatic malt will give the starter more food to munch on, and add flavor as well.
Many people just store their starter in a covered crock, leaving it at room temperature all of the time. They feed it regularly and use it frequently. This is necessary because as the yeast eats the sugars, and starches, it gives of acids, hence the sour flavor in sour dough. Though wild yeast is more tolerant of acidic environments, it too can only survive up to certain acid levels. By using the starter frequently, you dilute the acid when you feed it again.
Hope this helps.
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