Where the couplet "Obedience brings success; exact obedience brings miracles" came from

According to Tanner Skousen, the phrase in question was spoken at an MTC talk given by Wendy Watson Nelson (not Elder) in May of 2011.

http://www.missionsite.net/eldertannerskousen/viewletter/105446

Elder Nelson’s use of the same phrase shows up in a talk there four months later and then again in an MTC talk given in 2013.

But it seems that the phrase did not originate with them.

Sister Nelson used it a second time in a Boulder Colorado Stake Fireside on Feb. 3, 2013. 

According to an article written about that talk Sister Nelson said that the phrase came out of a conversation between a mission president and a missionary. And it was the young missionary who coined the couplet.

https://communityblogconsiderthis.wordpress.com/2013/02/04/how-to-obtain-miracles/

So why is this couplet still being bandied about in regards to the gospel?

I think this is another case of a catchy phrase being picked up because it’s catchy and arresting and then getting out of hand.

Moral of the story: think very carefully before you use a catchy phrase in a talk.