What does Imam al-Husayn mean by his saying, “I did not go out in exultation or in arrogance…”, and does it have a bearing on one's personal life?

The saying mentioned came in a letter written in the hand of Imam al-Husayn (a), addressed to his brother Muhammad ibn al-Hanafiyya (r). It is the letter through which the Imam expressed the aims of the Husayni uprising. Perhaps the Imam chose that it be written, unlike the sermons he used to deliver, so that it would be more firmly established and lasting; and likewise [he chose] to hand it to Muhammad ibn al-Hanafiyya because his was the trustworthy hand that would preserve it. All of that is because this letter contained the fundamentals of the movement, while the rest of the sermons are a branching out and elaboration of what is in this important letter.

The Imam deliberately mentioned within it that his noble going out was not motivated by haughtiness, arrogance, showing off and seeking repute: ashar is exultant merriment (marah), and batar [describes] the arrogant one whom self-conceit has taken possession of. Rather, the going out was with a sincere intention, devoted purely to Allah the Exalted, seeking reform and rejecting corruption.

By this indication he affirms the necessity of declaring one's intentions; likewise, the believer must realize in himself sincerity toward Allah the Exalted before every act he performs. As has been narrated from al-Rida, from his forefathers (a), who said: Al-Sadiq (a), when he went out to prayer, used to say: “O Allah, I ask You by the right of those who ask of You, and by the right of this going out of mine, for I have not gone out in exultation, nor in arrogance, nor for show, nor for repute, but I have gone out seeking Your good pleasure and avoiding Your displeasure; so keep me safe, with Your safekeeping, from the Fire.”

So on the personal level, a person needs to realize in himself the required sincerity; and if the project he undertakes is a project that concerns society, he should inform them of that as well.

Moreover, the Imam's (a) declaration that he did not go out in exultation or in arrogance is an allusion to the Qurʾanic call in the words of the Exalted:

“Do not be like those who left their homes vainly and to show off to the people, and to bar [other people] from the way of Allah, and Allah comprehends what they do.” (Qurʾan 8:47), and thereby he reinforces the Qurʾanic frame of reference in his noble discourse.

However, what proves the truthfulness of the Imam (a)—and he is the truthful one (al-siddiq)—is that he did not describe his movement in this way in order to tell the people, “Submit to this,” even though he is an Imam whose obedience is obligatory; rather, his discourse constitutes a proof [binding] upon the generality of Muslims. So all he did was set for them the true scale, namely his words: “Whoever accepts me by accepting the truth—Allah is more worthy of the truth.” This expression is a proof of truthfulness, because he made the axis of accepting his movement a divine axis, that is: make the truth your criterion, for if you know the truth you will know its people, who carry its banner. This confidence is something none dare show except the sincere among those engaged in [such] movements; as for the pretenders and those who show off, they conceal this criterion from people, and even prevent them from being forthright in thinking and choosing on clear divine foundations.

As the Umayyads did: they used to conceal the criteria of polytheism (shirk), so that people would not hold them to account and evaluate them according to those criteria.

In al-Kafi, from Abu ʿAbd Allah (a), who said: “The Umayyads left people free to teach faith, but did not leave them free to teach polytheism, so that when they drove them to it, they would not recognize it.”