As they walked in the store,the clerk came to greet them.wal

As they walked in the store,the clerk came to greet them.
came to方向是“来”,此句侧重点是the clerk 朝them“走来”,说话者此时站的位子在“them”这边.
walk to方向是“去”,侧重点是说话者站在动作者的位子说.
如：As the clerk saw them come in the store,he walked to greet them.