The differences between the two include scope of application and visual elements.

1. Scope of application: "Regroup" is mostly used for individuals or small groups, emphasizing personal determination and willpower. "Revival" is more suitable for larger organizations or groups, such as companies, government agencies, etc.

2. Visual elements: The expression "regroup the flag and drum" has a more visual element, in which "flag and drum" refers to the flags and drums in ancient wars, which represent command and morale. This phrase uses figurative elements to convey the meaning of regrouping strength and preparing to start again. Although "revive the flag and drum" also has the meaning of revitalization, it does not contain as much figurative elements as "regain the flag and drum".