This has jewish roots:
chabad.org/library/article_cdo/aid/562222/jewish/Is-it-okay-to-ask-a-deceased-tzaddik-to-pray-on-my-behalf.htm/mobile/false
Well, let me ask…do you think Christ would stop guiding the Church in this regard?
Here is an indepth explanation:
calledtocommunion.com/2009/08/a-catholic-reflection-on-the-meaning-of-suffering/comment-page-1/#comment-7404
How can a saint in heaven hear our prayers? Saints are not omniscient or omnipresent; only God is omniscient and omnipresent. So how can they seemingly have such abilities?
The saints in heaven can hear/see our requests to them, though not with physical ears/physical eyes (since they are not embodied, Mary excepted). In three places in the gospels, Jesus tells us that in the resurrection we will be like the angels. One of the ways in which we will be like the angels is that we will not marry. But another way is that we will know, not only by our physical senses, but in a supernatural way, i.e. a way that exceeds the capacity of our epistemic faculties. All the angels and saints presently enjoy the Beatific Vision. (See Benedictus Deus.)
When a person has the Beatific Vision, he not only knows God; he also knows what pertains to himself, through God.
St. Thomas Aquinas explains:
The Divine essence is a sufficient medium for knowing all things, and this is evident from the fact that God, by seeing His essence, sees all things. But it does not follow that whoever sees God’s essence knows all things, but only those who comprehend the essence of God [Cf. I, 12, 7,8]: even as the knowledge of a principle does not involve the knowledge of all that follows from that principle unless the whole virtue of the principle be comprehended. Wherefore, since the souls of the saints do not comprehend the Divine essence, it does not follow that they know all that can be known by the Divine essence–for which reason the lower angels are taught concerning certain matters by the higher angels, though they all see the essence of God; but each of the blessed must needs see in the Divine essence as many other things as the perfection of his happiness requires.
As St. Thomas explains, anyone who sees the face of God sees also in God all things pertaining to himself, through God. The petitions of the members of the Church militant, pertain to the saints in heaven. And for this reason they see these petitions supernaturally, through the Beatific Vision.
Notice also in the selection from St. Thomas that he points out that “it pertains to their glory that they assist the needy for their salvation.” God doesn’t need the saints to intercede for us. He has given them a great gift, in allowing them to participate in this glorious way, in His work of redemption.
Because God is love, He does not do everything Himself. He created us, and gave us real causal powers. So, He doesn’t operate by the principle, “If I can do it, then there is no point in having anyone else do it.” He works by love, which is the very opposite of such egoism, because by love He gives to us the dignity of participation in His glorious activity. This is what we mean in speaking of His love as self-effusive. Strictly speaking, God did not need to give us causal powers of any sort. God could have done everything, entirely, Himself. He loves to give to us the opportunity to participate as real [secondary] causes in His work. That’s one of the gifts He has given to the saints in heaven, by allowing them to be genuine intercessors on our behalf.