The Messenger of Allah (may Allah's peace and blessings be upon him) said: "My advent and the Hour are like these," and he pointed with his two fingers

The Prophet (may Allah's peace and blessings be upon him) informs us in this Hadīth about the approach of the Day of Judgment. The start of His mission and the Day of Judgment are as close as his two fingers are to each other, and he pointed with them, stretching them out, to make them distinct from his other fingers.
In some other Hadīths, it was mentioned that those two fingers were the index and middle fingers, which are very close when joined, with only the length of a nail or even half a nail between them. The index finger is called Sabbābah because if one wants to insult (Sabb) someone, he points at him with that finger. Moreover, it is also called Sabbāhah because one raises that finger when he glorifies Allah, Exalted and Glorified, pointing at the sky. The Hadīth highlights, in brief, the fact that the worldly life is short and will soon come to an end.