First posted May 2010.
In 1905 a man named John Sampson published The Poetical Works of William Blake, said to be the first complete edition. Blake commentary and criticism took off at that point.
In ca 1920 S. Foster Damon came forth with William Blake: His Philosophy and Symbols, a rare book nowadays. On Page 316 he stated that Plate 2 of The Marriage of Heaven and Hell was written in light of Isaiah 35. It echoes the 35th chapter of Isaiah. The "way of holiness" is what Blake called the perilous path.
Here's Plate 2 of MHH.
" THE MARRIAGE of HEAVEN and HELL PLATE 2 The Argument. Rintrah roars & shakes his fires in the burdend air; Hungry clouds swag on the deep Once meek, and in a perilous path, The just man kept his course along The vale of death. Roses are planted where thorns grow. And on the barren heath Sing the honey bees. Then the perilous path was planted: And a river, and a spring On every cliff and tomb; And on the bleached bones Red clay brought forth. Till the villain left the paths of ease, To walk in perilous paths, and drive The just man into barren climes. Now the sneaking serpent walks In mild humility. And the just man rages in the wilds Where lions roam. Rintrah roars & shakes his fires in the burdend air; Hungry clouds swag on the deep."
This gave me a sudden enlightenment when I realized that Blake here was giving a critique of Isaiah 35 and following chapters. Immediately after the "way of holiness" Isaiah gives the ominous warning of Sennacherib, leading to King Hezekiah's famous verse: "not in my time, Lord."
Isaiah 35 The wilderness and the solitary place shall be glad for them; and the desert shall rejoice, and blossom as the rose.
 It shall blossom abundantly, and rejoice even with joy and singing: the glory of Lebanon shall be given unto it, the excellency of Carmel and Sharon, they shall see the glory of the LORD, and the excellency of our God.
 Strengthen ye the weak hands, and confirm the feeble knees.
 Say to them that are of a fearful heart, Be strong, fear not: behold, your God will come with vengeance, even God with a recompence; he will come and save you.
 Then the eyes of the blind shall be opened, and the ears of the deaf shall be unstopped.
 Then shall the lame man leap as an hart, and the tongue of the dumb sing: for in the wilderness shall waters break out, and streams in the desert.
 And the parched ground shall become a pool, and the thirsty land springs of water: in the habitation of dragons, where each lay, shall be grass with reeds and rushes.
 And an highway shall be there, and a way, and it shall be called The way of holiness; the unclean shall not pass over it; but it shall be for those: the wayfaring men, though fools, shall not err therein.
 No lion shall be there, nor any ravenous beast shall go up thereon, it shall not be found there; but the redeemed shall walk there:
 And the ransomed of the LORD shall return, and come to Zion with songs and everlasting joy upon their heads: they shall obtain joy and gladness, and sorrow and sighing shall flee away.
 And the remnant that is escaped of the house of Judah shall again take root downward, and bear fruit upward:
 For out of Jerusalem shall go forth a remnant, and they that escape out of mount Zion: the zeal of the LORD of hosts shall do this.
 Therefore thus saith the LORD concerning the king of Assyria, He shall not come into this city, nor shoot an arrow there nor come before it with shields, nor cast a bank against it.
 By the way that he came, by the same shall he return, and shall not come into this city, saith the LORD.
 For I will defend this city to save it for mine own sake, and for my servant David's sake.
 Then the angel of the LORD went forth, and smote in the camp of the Assyrians a hundred and fourscore and five thousand: and when they arose early in the morning, behold, they were all dead corpses.
 So Sennacherib king of Assyria departed, and went and returned, and dwelt at Nineveh.
 And it came to pass, as he was worshipping in the house of Nisroch his god, that Adrammelech and Sharezer his sons smote him with the sword; and they escaped into the land of Armenia: and Esar-haddon his son reigned in his stead.
Of course if you've read The Marriage of Heaven and Hell, you recall that Blake reported a vision in which he dined with and interviewed Isaiah and Ezekiel. Go to plates 12 and 13.