It is related that our Prophet (saas) said: Doomsday will not take place until the Qaim [Hazrat Mahdi (as)], my descendant, appears. This will be a time permitted by Allah.  Those who follow him will be saved, while those who hang back will be perished. O servants of Allah! Fear Allah: WHEN HAZRAT MAHDI (AS) APPEARS, ABANDON EVERYTHING AND RUN TO HIM BY ALL POSSIBLE MEANS. Because he is the caliph of Allah (Muslims' spiritual leader) and my heir. (Bihar al-Anwar, Vol. 51, P. 65; Ithbat-ul Hudat, Vol. 6, p. 382)

... If Allah permits you to see this RUN TO SWEAR ALLEGIANCE TO HIM (FOLLOW HIM) AND NEVER ABANDON HIM. IF YOU ARE SUCCESSFUL, NEVER ABANDON HIM IF YOU REACH HIM AND FIND THE TRUE PATH. Ah - and he pointed to his chest - how I long to see him." (Sheikh Muhammad bin Ibrahim Nomani, al-Ghaybah al-Nomani, p. 252)

LET NOTHING HOLD YOU BACK FROM SWEARING ALLEGIANCE TO HIM (FROM BEING HIS FOLLOWER, FROM FOLLOWING HIM) those who hold you back are those who have always sought refuge in corruption. If they speak, they speak evil, and if they are silent, they are impious and perverse.  (Sheikh Muhammad bin Ibrahim Nomani, al-Ghaybah al-Nomani, p. 252)