Paul wrote:
"Now we beseech you, brethren, by the
coming of our Lord Jesus Christ, and by
our gathering together unto him,
That ye be not soon shaken in mind, or
be troubled, neither by spirit, nor by word,
nor by letter as from us, as that the day of
Christ is at hand." 2 Thessalonians 2:1-2

He admonishes the believers not to be
deeply troubled by believing that the Day
of the Lord had come upon the world.