Question:

When is the Messiah finally going to arrive?

Answer:

Moshiach could potentially come at any moment, as his arrival depends upon our actions. 

The Torah says (Deut. 30:2), "[When] you will return unto the Lord, your G-d, and listen to His voice, according to everything that I command you today . . with all your heart and all your soul. Then the Lord, your G-d, will bring back your captivity and have mercy upon you. And He will gather you in from all the nations..."

Rabbi Joshua Ben Levi once approached Moshiach and asked him, "My master, when are you coming?"  Moshiach answered, "today!"  When the day passed with no signs of Moshiach's revelation, R. Joshua disappointedly returned to him and asked why he had not kept his word.  Moshiach said, "Indeed, I will come today - if you hearken to His voice." 

Moshiach could potentially come at any moment, as his arrival depends upon our actions.  Over the many generations of exile, we have completed our task of refining the world.  In our generation, all the preparatory work has been done, and we only await Moshiach's actual revelation.  We do not know what, exactly, will be the trigger that will usher in the Messianic era.  A single good deed, done by one individual, could be the key to bring redemption to all of humanity.  Thus, we must live each day expecting that Moshiach will actually arrive this very day. 

The LubavitcherRebbe, Rabbi Menachem M. Schneersohn, has prophetically informed us that we are currently living in the generation of the messianic redemption. It is our obligation to increase our acts of goodness and kindness to hasten his revelation.