The Holy Imam (as) wanted to let those who had joined him...
The Holy Imam (as) wanted to let those who had joined him for the sake of worldly position, power and money quit the battleground. Additionally, the presence of people lacking strong motivation and character can harm an army and is not beneficial. This is because such people spread the fear and uncertainty which they feel in their hearts to the other soldiers in the camp. This reduces the morale and discipline of the entire army.
Fear is contagious and can cause irreparable division among the soldiers of an army. We can also infer that Imam al-Husayn (as) was inspiring his true companions with this kind of discourse to strengthen their determination for war. He was stimulating his true and loyal companions to be even more steadfast in his defence.
We can deduce that because the tents were pitched close to each other and the people could hear each other’s voices, Imam al-Husayn (as) wanted his family members to hear for themselves the answers that would be provided by his loyal and faithful companions. This would warm their hearts and raise their spirits high. We can infer that with his speech Imam al-Husayn (as) intended to motivate his followers for a holy war and free them from tribal and clan bigotry.
He wanted them to defend him not because of tribal ties, but out of divine motivation to defend what is right and true. He wanted to motivate them to come to the defence of Islam, the faith and monotheism. Imam al-Husayn’s (as) aim when he made his speech was not to acquit his companions from duty and obligation. In these sensitive circumstances, no one had any pretext for leaving his Imam alone when he needed their help the most.
In reality, the battle that Imam al-Husayn (as) was involved in was such that there was no need for him to ask for help from his companions. Everyone was duty-bound to aid the Holy Imam (as). The very fact that Imam al-Husayn (as) found himself in these circumstances is a call of invitation for help. Is it not incumbent upon people to protect the life of Allah’s trust on earth?
When Imam al-Husayn (as) witnessed that his companions possessed sincere and honest intentions, he prayed for them and said, “Lift your heads to the sky and see for yourselves.” When they looked up, they observed their places in heaven. We can deduce from this that Imam al-Husayn (as) wanted to get their allegiance and loyalty before showing them their places in heaven.