One starting point would be 1 Thessalonians, 4:14
For since we believe that Jesus died and rose again, even so, through Jesus, God will bring with him those who have fallen asleep. [RSV]
For a Catholic, a Saint is someone whose life bears witness that they have already risen again, and are declared to have been already judged, and found to be sufficiently holy that they are already in heaven with God, living eternal life in Heaven. The people who are in Heaven, are alive, just like you and I are, and not dead. Such individuals would not only include Jakov (Jacob) the patriarch, and the other Patriarchs of—Abraham, Israel, Isaac, and Moses (among others) but more recent individuals, including David the King, and much more recent individuals such as Theresa of Calcutta. Because these people are not dead, but alive eternally in God's presence, the Church calls them Saints. Because they are alive, asking for them for "favors" on our behalf, or on the behalf of others, is not considered to be praying to the dead, but rather the same as someone asking you to pray for them.