Think good; Will be good!
God gave us "Freedom of Choice". We express this freedom in 3 ways:
Free to think thoughts of one thing or another;
Free to speak words of one sort or another;
And free to do, one way or another.
In 3 ways we can align with, or misalign with, a given perspective.
You can think good thoughts or bad thoughts.
You can say good things or bad things, and
you can do either good or bad.
Thinking, saying and doing are referred to in chassidus as "garments". Just as you can choose which garment to wear or shed, so too you can decide to "wear" new thoughts and thereby abandon ("shed") your former thoughts; As you can say words that please in place of words that displease; And you can do favors and avoid crime, instead of proceeding otherwise.
Can emotions also be referred to as "garments"? No! There's no "free choice" for emotions. Emotions pursue thought, and not the other way around. Thoughts evoke emotions.
However, because emotions follow reflexively from thoughts, the garment of thought can be changed. This change of thoughts will trigger new emotions to supplant those that preceded.
Free choice, in light of chassidus, subdivides into thoughts, speech and behavior.
That bit of chassidus also sheds light on how to control emotions.
The Rebbe so instructed us because he wanted us to see spectacles we'd otherwise never sense. Our panoramas are vast and exactly what to look for in this broad landscape to discern a moving target, among lots of activity, needs special attentiveness.
Learning about Moshiach and speaking and doing about Moshiach grows spiritual antennas. There are things happening locally and globally and to feel good amid these swirling events -- to be able to connect the dots of all these events in a refreshing light, they must be identified in proper context.
In other words, if we believe the Rebbe and do as he wishes, we'll discover that worldly events, which happen beyond our control, are actually benefiting us. We can begin to appreciate the good the Rebbe wants us to experience these days, much as father wants to impart his love to his child.
For those who think thoughts devoid of Moshiach, or have an entirely different perspective, the lesson of the Rebbe will be missed by them. Here's an example of this phenomenon today: What might appear to one person as a political fluke, as it might concern a politically-immersed person of the Democrat party, say regarding president Trump's election win in 2016, and he's expecting that already in 2020 Trump will be replaced by a "suitable" candidate -- to another person is a laughing joke. This other person, well-versed in Torah's views on Moshiach, sees that event as a palpable marker of a new era in history. This event was not at all a fluke. Rather, it was a sharp upturn in Moshiach's momentum.
This is an example of how "garments" of thought give one person agony for 4 long years, and to the other sheer ecstasy, under the same circumstances, seeing an altogether different pattern in the mosaic developing before him.
One will wallow while the other will thrive under the same circumstances. Think good; Will be good. Think Moshiach; Will sense Moshiach's imminence!