Ego, conniving, and backstabbing. Or, as it's called in the
Pearson Darby offices, just another day on the job. 
Harvey is still attempting to become a managing partner to take down Jessica. Rachel finds out about the roles that Mike, Donna and Harvey played in breaking Mike and herself up originally. And just to drive the theme home, the case that Harvey is working on centers around testimony that an oil company's number two offers up against his boss and mentor.
But amidst the backstabbing and bruised egos is the desire for forgiveness. One example of this is Mike and Harvey finally make up. I'd say spoiler alert, but you knew it was coming. Did you really think that they'd let Mike work for Louis? I didn't think so. Yes, it takes until the end of the episode and occurs only after Mike had agreed to work for Louis, but it happens. Is the forgiveness perfect? No. Harvey only agrees to forgive Mike after Mike has begged and pleaded (for basically the whole season) and after Mike has proved time and again his usefulness. For Harvey, Mike is a tool that is too valuable to discard though, as the final scene's reuniting handshake evidences, has a tinge of sentimental value as well.
Not all relationships are so neatly cleaned up by the end of the episode, however. Harvey, despite forgiving Mike, still seeks to take down Jessica. The client guilty of the bribe has still lost her protegee. And Louis Litt's heart is broken after Mike goes back on his word, abandoning Team Litt for Team Harvey.
As the episode ends, not all is well in the world of Pearson Darby, but with the reunification of Harvey and Mike, at least some level of normalcy has returned.