In Catholicism, what is the conceptual relationship between prayer on behalf of the departed and prayer to the departed?

One of the many important areas of disagreement between Catholicism and Protestantism is how the two understand the intercession of the saints. Both groups agree that saints in heaven may pray to God on behalf of the Church on earth. However, Catholics believe that it is appropriate for Christians alive on earth now to ask the saints in heaven to pray for us, whereas Protestants do not think so. In defense of their view, Catholics often cite 2nd Maccabees 12:39-46, which reads in the *New American Bible:* > 39 On the following day, since the task had now become urgent, Judas and his companions went to gather up the bodies of the fallen and bury them with their kindred in their ancestral tombs. 40 But under the tunic of each of the dead they found amulets sacred to the idols of Jamnia, which the law forbids the Jews to wear. So it was clear to all that this was why these men had fallen. 41 They all therefore praised the ways of the Lord, the just judge who brings to light the things that are hidden. 42 Turning to supplication, they prayed that the sinful deed might be fully blotted out. The noble Judas exhorted the people to keep themselves free from sin, for they had seen with their own eyes what had happened because of the sin of those who had fallen. 43 He then took up a collection among all his soldiers, amounting to two thousand silver drachmas, which he sent to Jerusalem to provide for an expiatory sacrifice. In doing this he acted in a very excellent and noble way, inasmuch as he had the resurrection in mind; 44 for if he were not expecting the fallen to rise again, it would have been superfluous and foolish to pray for the dead. 45 But if he did this with a view to the splendid reward that awaits those who had gone to rest in godliness, it was a holy and pious thought. 46 Thus he made atonement for the dead that they might be absolved from their sin. I don't see what the connection is. I would think that people on earth praying for the deceased is the opposite of people on earth praying to saints in heaven. In the former case, it is *our* prayers which are meant to be helpful to *them*. In the latter, it is *their* prayers which are meant to help *us*. Furthermore, in the former case there is no communication between the living and the dead, quite unlike the idea of directing prayers towards people in heaven. (And that is a very important detail, as that is the point of divergence between Catholic and Protestant regarding the Intercession of the Saints.) The footnote in the 2012 *New American Bible* also makes no reference to prayers to the saints on these verses: > This is the earliest statement of the doctrine that prayers (v. 42) and sacrifices (v.43) for the dead are efficacious. Judas probably intended his purification offering to ward off punishment from the living. The author, however, uses the story to demonstrate belief in the resurrection of the just (7:9, 14, 23, 36), and in the possibility of expiation for the sins of otherwise good people who have died. This belief is similar to, but not quite the same as, the Catholic doctrine of purgatory. So basically, I do not see how the practice of praying *to* people in Heaven is similar to praying *on behalf of* people in Purgatory. **I would like some clarification on the purported connection between the two concepts.**