Paul is drawing a conclusion based on the authority of Isaiah and David.
From the beginning of the Chapter, he says presents that the fall of the Jews is not universal. The conclusion you want to understand presents envy of the Jews by
the withdrawing of grace: “God has given them the spirit of insensibility”, or as you seem to put it deep sleep.
“Likewise it says in Isaiah: ‘make the heart of this people fat, and their eyes heavy, and shut their eyes; lest they see with their eyes and hear with their ears’ (Isa 6:10). And in regard to this he designates their weakened power of knowing, when he adds eyes that they should not see the miracles which Christ performed in their presence, and ears that they should not hear fruitfully the teachings of Christ and the apostles: ‘you that see many things, will you not observe them? You that have ears open, will you not hear?’ (Isa 42:20).” (St. Thomas Aquinas, Rom. C. 11 L. 1, 875)
This answer is based on the interpretation of the Angelic Doctor.
https://aquinas.cc/196/198/~2995
It shows the misery of withdrawing from the sacraments or grace of God, which are the way, in that which we read from Jesus, I am the way, the truth, and the life. (Cf. St. Bonaventure, Disputed Questions on Evangelical Perfection, q. 1, c.; St. Bernard, The Steps of Humility and Pride, 1, 1)