"The greater the charity of the Saints in their heavenly home,
 the more they intercede for those who are still on their journey

 and the more they can help them by their prayers;
 the more they are united with God, the more effective those prayers are.
 This is in accordance with Divine order, which makes higher things react upon lower things,
 like the brightness of the sun filling the atmosphere."
St. Thomas Aquinas, O.P.