It’s literally presented in the novel that Mercerism’s teachings were to preserve life on earth, how ever little of it was left; but, in underlying objection to technology, it’s intent was more specifically meant to eliminate the future and the elimination of the thought process in looking forward, since this wrought the planet in it’s current state.

Preservation of life is a by product of eliminating advancements of society because it all led to the end of the world, which is why Mercer agrees with Rick in retiring the androids. Mercer outright told Rick that he was doing the right thing when eliminating the androids, that he condoned doing it even if Rick had some form of objection through his empathy of Pris (how she is similar in model to Rachael, who he had feelings for). And Rick finally “becomes” Mercer when he visits that hill and is permanently fused with Mercer afterwards (P.231, P.233). His “permanent fusion” is essentially Rick reflecting on how he is not interested in preserving life, he is interested in preserving humanity.

“So this is what Mercer sees, he thought as he painstakingly tied the cardboard box shut–tied it again and again. Life which we can no longer distinguish; life carefully buried up to its forehead in the carcass of a dead world. In every cinder of the universe Mercer probably perceives inconspicuous life. Now I know, he thought. And once having seen through Mercer’s eyes, I probably will never stop.

And no android, he thought, will cut the legs from this. As they did from the chickenhead’s spider.” P.238

Rick realizes that humanity is endangered, much like the toad he found on his trail. The androids are taking over as the driving force of technological progress when the past is being left behind to die and be abandoned (like the colonies did when leaving the earth). “Life which we can no longer distinguish; life carefully buried up to its forehead in the carcass of a dead world” is the most exceptionally poignant part of this passage, because you could categorize what the Android’s strive for is life, but it’s not exceptionally distinguishable to human life since life emanates from us beyond just one person; we are communal creatures who work together and life flourishes from this community onto the planet. The health of the planet is reflective of the health of mankind and their ability to be together in preservation of life, whereas the Androids see life as a utility (like with Isidore’s spider and the cutting of legs because it was not “practical”).

This endangerment in humanity is even more clearly shown through the discovery that the toad was in fact a fake:

“‘Maybe I shouldn’t have told you–about it being electrical.’ She put her hand out, touched his arm; she felt guilty, seeing the effect it had on him, the change.

‘No,’ Rick said. ‘I’m glad to know. Or rather–’ He became silent. ‘I’d prefer to know’

…’The spider Mercer gave the chickenhead, Isidore; it probably was artificial, too. But it doesn’t matter. The electric things have their lives, too. Paltry as those lives are.’” P.241

The realization that the toad is fake brings Rick back into the reality that his and all of humanity’s days are numbered, that machines with their inevitable ability to mimic humanity perfectly will cause the death of humanity. Humanity already killed the earth, and humanity with it’s technological progress will also eliminate humans from existence if it continues the way it does.

Life will go on in the form of Androids, and ultimately Rick and the rest of society in DADoES accepts that, even Mercer from the previous quote where he gave Rick and Isidore fake animals to find in the environment, and in this quote:

“‘The killers that found Mercer in his sixteenth year, when they told him he couldn’t reverse time and bring things back to life again. So now all he can do is move along with life, going where it goes, to death. And the killers throw the rocks; it’s they who’re doing it. Still pursuing him. And all of us, actually. Did one of them cut your cheek, where it’s been bleeding?’” P.242-243

Mercer has no choice but to move on with life in how it’s progressing, and it’s progressing in the form of Androids being the next species to be on top of the living food chain.

On the final page of the novel, when Iran is ordering all the amenities for the artificial toad and all the specific needs that the clerk talks about for the fake toad (from the synthetic food to the perpetually renewing puddle), this subtly ends the novel with a dark, underlying message that we can’t fight against technology and it’s progression. Inevitably, life will be made around technology rather than we maintain life with the use of technology…