Honestly, it goes even further than that. The generally accepted theory in the Lion Air incident is that a system caused MCAS might be one of the major causes of the accident.
Basically, the larger/more powerful/further forward engines on the MAX would cause the airplane to behave differently to other 737 variants in some situations, and MCAS is designed augment pilot input and allow the pilots to fly the planes as they would have flown other 737s (and allows pilots to fly MAXes under the same type ratings as previous 737 models). However, in edge cases (in the case of Lion Air, erroneous sensor input) the airplane might do something totally different from other 737 variants. Evidently Boeing didn't even require pilots to be told about MCAS, because all it (supposedly) does is make a MAX feel like an older 737.
Basically, the larger/more powerful/further forward engines on the MAX would cause the airplane to behave differently to other 737 variants in some situations, and MCAS is designed augment pilot input and allow the pilots to fly the planes as they would have flown other 737s (and allows pilots to fly MAXes under the same type ratings as previous 737 models). However, in edge cases (in the case of Lion Air, erroneous sensor input) the airplane might do something totally different from other 737 variants. Evidently Boeing didn't even require pilots to be told about MCAS, because all it (supposedly) does is make a MAX feel like an older 737.