Appamāda - What is it? How to practise it? Benefits?

In this video , Ven. Yuttadhammo Bhikkhu says that the whole of the Buddhist teachings could be summarized as Appamāda (heedfulness), at the risk of oversimplification. In the Mahaparinibbana Sutta (DN16) , the Buddha conveyed the last message of his life: > Then the Blessed One addressed the monks, "Now, then, monks, I exhort > you: All fabrications are subject to decay. Bring about completion by > being **heedful**." Those were the Tathagata's last words. According to the Appamāda Sutta (SN3.17) : > "There is one quality, great king, that keeps both kinds of benefit > secure — benefits in this life & benefits in lives to come." > > "But what, lord, is that one quality...?" > > "**Heedfulness**, great king. Just as the footprints of all living > beings with legs can be encompassed by the footprint of the elephant, > and the elephant's footprint is declared to be supreme among them in > terms of its great size; in the same way, **heedfulness** is the one > quality that keeps both kinds of benefit secure — benefits in this > life & benefits in lives to come." Questions: 1. What really is Appamāda (heedfulness)? 2. How does one practise Appamāda (heedfulness)? 3. What are the benefits of Appamāda (heedfulness)? 4. Why is this one of the most important concepts in Buddhism, that the Buddha chose this to be his last message? 5. What is the relationship between Appamāda (heedfulness) and mindfulness? This answer equates the two.