From a Catholic viewpoint, why will there be a particular judgement and a general judgment? If we are judged by God at the moment of death, why is Jesus, at his Second Coming going to judge the living and the dead at the Last Judgment?
Catechism of the Council of Trent (The Roman Catechism) "Article 7: From thence he shall come to judge the living and the dead.:"


  Reasons For General Judgment
  
  It is necessary to show why, besides the particular judgment of each
  individual, a general one should also be passed upon all men.
  
  Those who depart this life sometimes leave behind them children who
  imitate their conduct, dependents, followers and others who admire and
  advocate their example, language and actions. Now by all these
  circumstances the rewards or punishments of the dead must needs be
  increased, since the good or bad influence of example, affecting as it
  does the conduct of many, is to terminate only with the end of the
  world. Justice demands that in order to form a proper estimate of all
  these good or bad actions and words a thorough investigation should be
  made. This, however, could not be without a general judgment of all
  men.
  
  Moreover, as the character of the virtuous frequently suffers from
  misrepresentation, while that of the wicked obtains the commendation
  of virtue, the justice of God demands that the former recover, in the
  public assembly and judgment of all men, the good name of which they
  had been unjustly deprived before men.
  
  Again, as the just and the wicked performed their good and evil
  actions in this life not without the cooperation of the body, it
  necessarily follows that these actions belong also to the body as to
  their instrument. It was, therefore, altogether suitable that the body
  should share with the soul the due rewards of eternal glory or
  punishment. But this can only be accomplished by means of a general
  resurrection and of a general judgment.
  
  Next, it is important to prove that in prosperity and adversity, which
  are sometimes the promiscuous lot of the good and of the bad,
  everything is done and ordered by an all-­wise and all­-just Providence.
  It was, therefore, necessary not only that rewards should await the
  just and punishments the wicked, in the life to come, but that they
  should be awarded by a public and general judgment. Thus they will
  become better known and will be rendered more conspicuous to all; and
  in atonement for the unwarranted murmurings, to which on seeing the
  wicked abound in wealth and flourish in honours even the Saints
  themselves, as men, have sometimes given expression, a tribute of
  praise will be offered by all to the justice and Providence of God. My
  feet, says the Prophet, were almost moved, my steps had well nigh
  slipped, because I had a zeal on occasion of the wicked, seeing the
  prosperity of sinners; and a little after: Behold! these are sinners
  and yet abounding in the world, they have obtained riches; and I said,
  Then have I in vain justified my heart, and washed my hands among the
  innocent; and I have been scourged all the day, and my chastisement
  hath been in the morning. This has been the frequent complaint of
  many, and a general judgment is therefore necessary, lest perhaps men
  may be tempted to say that God walketh about the poles of heaven, and
  regards not the earth.