not to be soon shaken in mind or troubled, either by spirit or by word or by letter, as if from us, as though the day of Christ had come.
2 Thessalonians 2:1-2 (NKJV)
While there are some things that need to be shaken to be effective, most things and people do not do well if they are shaken up. Shaking someone, as in an earthquake, rocking them back and forth in a violent manner, or forcing them up and down repeatedly, will have a negative effect on them. If something or someone has been shaken too much, then something needs to be done to stabilize that thing or person. We all need physical stability and security, without that, there can be a multitude of problems.
When he wrote his second letter to the Thessalonians, Paul let them know that he did not want those people to be shaken or troubled in any way. It seems that somehow some wrong teaching had come to the Thessalonian believers, and the results were not good. When there is wrong teaching, there will be instability, and people can become shaken and troubled. Paul did not want them to remain in this position but to be stable, and he wanted to stop the shaking, so to speak, by giving them some right teaching.
Although Paul was specifically writing to the Thessalonians and encouraging them to not be shaken or troubled concerning the return of Jesus, this same thing happens in other areas too. When Christians are not sure what is right and wrong, they can be shaken, and they are then not doing the things that they should be doing. The solution is to give people correct teaching of Bible truths to counter the wrong teaching that has caused the shaking and the trouble. We should not be shaken, but we need to be stable, solid Christians who do God's will.