How can one get rid of intense envy and jealousy, the thought that one will not attain Allah's grace due to sins, and the feeling of an insurmountable barrier between the servant and his Lord?

You must repent immediately from sins, especially abandoning prayer and disobedience to parents. Purify your repentance so that its purpose is to please Allah, not the pleasures of this world. Know that the expansion or constriction of worldly provisions is not the sole proof of Allah's contentment, but sins do have effects in constricting sustenance. The expansion of blessings might also be a test. The causes of envy stem from self-exaltation, arrogance, fear of losing what is desired, love of leadership, malice, and rancor. Your feeling of a barrier between you and your Lord might be due to the ill effects of sins, which engender a sense of desolation in the heart.