‘Now there came a famine over all Egypt and Canaan, and great affliction: and our fathers found no sustenance, and when Jacob heard that there was grain in Egypt, he sent forth our fathers the first time.'
Meanwhile the whole world was suffering from famine so that ‘our fathers' (note the more personal application, referring it to the ones from whom ‘we' come and whom ‘we' are like) found no sustenance. And the result was that hearing of grain in Egypt Jacob sent forth ‘our fathers' the first time. The relation of famine to spiritual dearth occurs often in the Old Testament, and to those who were used to dealing in allegories the point would hardly be missed. Those who appeared to be God's faithful ones, who were suffering spiritual famine because they had refused to hear God's prophet, would have to look to ‘outside' sources for their sustenance. Their own were insufficient. God neither heard in their land, nor responded to their pleas at their altar.
But when they went forth the first time they did not recognise their deliverer for who he was. This is implied by the silence. They sought sustenance but did not recognise the source. Yet the source should have been known to them. It was in their blindness that they did not know him. Yet from him alone was there life.
It will be noted that we are here pressing home the applications. Stephen was quietly allowing them to sink in.