Collation means "to bring together" or "a light meal," and it is a further attempt at remembering the deceased, closure for family and friends, and dispelling grief after the funeral gathering.
People will laugh, cry, argue, get angry or just feel numb, but the gathering may ease suffering of the loved ones of the deceased.
People who come to the reception show love and respect for the deceased person's loved ones by offering comfort and companionship. Memories of this celebration can lift spirits and ease loneliness and grief in the bleak months that follow.
Food and eating is a celebration of life, food is life sustaining - quite the opposite of death. the loved one is gone, but people left behind have to find a way to go on. Eating is one symbol of continued life, nourishment, sustaining oneself.
II suppose the only thing worse than having to go through the collation, is not going through it.