This morning two events coincided that sent me looking for this sutta.
One was this quote by Bhante Sujato
And the second was the closest encounter with a large tiger snake I have ever had (and I’ve had a lot). It was a fair call that I wouldn’t be writing this post now 
Life is precarious, but often we live like there is always going to be a tomorrow, putting off the important things. Are you ready to be dead? As the Buddha outlines, reflection on this is a great spur to practice.
It is a beautiful and inspiring sutta - For those not familiar with it, I hope it transfers some energy and urgency your way 
Mindfulness of death (2nd) AN 6.20
At one time the Buddha was staying at Nādika in the brick house. There the Buddha addressed the mendicants:
“Mendicants, when mindfulness of death is developed and cultivated it’s very fruitful and beneficial. It culminates in the deathless and ends with the deathless. And how is mindfulness of death developed and cultivated to be very fruitful and beneficial, to culminate in the deathless and end with the deathless?
As day passes by and night draws close, a mendicant reflects: ‘I might die of many causes. A snake might bite me, or a scorpion or centipede might sting me. And if I died from that it would be an obstacle to me. Or I might stumble off a cliff, or get food poisoning, or suffer a disturbance of bile, phlegm, or piercing winds. And if I died from that it would stop my practice. ’ That mendicant should reflect: ‘Are there any bad, unskillful qualities that I haven’t given up, which might be an obstacle to me if I die tonight?’
Suppose that, upon checking, a mendicant knows that there are such bad, unskillful qualities. Then in order to give them up they should apply outstanding enthusiasm, effort, zeal, vigor, perseverance, mindfulness, and situational awareness. Suppose your clothes or head were on fire. In order to extinguish it, you’d apply intense enthusiasm, effort, zeal, vigor, perseverance, mindfulness, and situational awareness. In the same way, in order to give up those bad, unskillful qualities, that mendicant should apply outstanding enthusiasm …
But suppose that, upon checking, a mendicant knows that there are no such bad, unskillful qualities. Then that mendicant should meditate with rapture and joy, training day and night in skillful qualities.
Or else, as night passes by and day draws close, a mendicant reflects: ‘I might die of many causes. A snake might bite me, or a scorpion or centipede might sting me. And if I died from that it would stop my practice. Or I might stumble off a cliff, or get food poisoning, or suffer a disturbance of bile, phlegm, or piercing winds. And if I died from that it would stop my practice. ’ That mendicant should reflect: ‘Are there any bad, unskillful qualities that I haven’t given up, which might be an obstacle to me if I die today?’
Suppose that, upon checking, a mendicant knows that there are such bad, unskillful qualities. Then in order to give them up they should apply outstanding enthusiasm, effort, zeal, vigor, perseverance, mindfulness, and situational awareness. Suppose your clothes or head were on fire. In order to extinguish it, you’d apply intense enthusiasm, effort, zeal, vigor, perseverance, mindfulness, and situational awareness. In the same way, in order to give up those bad, unskillful qualities, that mendicant should apply outstanding enthusiasm …
But suppose that, upon checking, a mendicant knows that there are no such bad, unskillful qualities. Then that mendicant should meditate with rapture and joy, training day and night in skillful qualities.
Mindfulness of death, when developed and cultivated in this way, is very fruitful and beneficial. It culminates in the deathless and ends with the deathless.”