I am currently reading a book by T. Austin-Sparks called "The Battle for Life". I had been seeing that we are all in a battle to retain our possessions (spiritual), we are all facing onslaughts of various kinds in these days. We really need to hold fast that which we have. I was led to get this book down off the shelf and am overpowered by the depth and strength of it.
Just before this quote, he had been talking about Zechariah 4 and the two living olive trees that continually pour the oil into the pipes to the bowls on the lampstand. They are living trees, not a cistern, but oil being poured continually, ever fresh, not stored up, and maintained at full strength continually. I think this also relates to the parable of the virgins. The marginal reading in Matthew 25 reads "our lamps are going out" which gives a good sense of this necessity of the continual need of the oil.
Here is the quote, I am sure this book is available, maybe even online, just do a search for T. Austin-Sparks---
The Undying Flame (from "The Battle for Life")
"It is the testimony of an unfailing life, an undying life, an all-sufficient life; the testimony of a life which is not an abstract, which is not something stored up, but something which is coming all the time from an inexhaustible stream; a mighty, glorious life. As the light burns, it is a constant declaration of victory, and that a victory over death, death which would seek to quench the light, quench the flame, smother it. It burns in the mist of surrounding death, a continuous declaration that death has no power to quench it."