Now will I rise. There is great force in the particle now, and likewise in the repetition which is added, "I shall be exalted, I shall be lifted up on high." We ought to observe the time to which these statements relate, that is, when the Church appeared to be utterly ruined; for God declares that he will judge that to be the most suitable time for rendering assistance. This is, therefore, a comparison of things which are contrary to each other; for he exhibits to believers the heavy and grievous calamities by which they should be oppressed, and under which they would easily sink, if they were not upheld by some consolation. As if he had said, "The Lord will suffer you to be brought very low, but when your affairs shall be at the worst, and when you shall have in vain tried every remedy, the Lord will arise and succor you." Thus even when we are afflicted and brought very low, we ought to acknowledge that our safety cometh from God alone. Accordingly, the word now denotes a period of the deepest distress. Men might think it exceedingly strange, but we plainly see the best reason why God thus delays to render assistance. It is, because it is useful to exercise the patience of the godly, to try their faith, to subdue the desires of the flesh, to excite to earnestness in prayer, and to strengthen the hope of a future life; and, therefore, he lays a restraint, that they may not with headlong eagerness anticipate that period which God has already marked out for them. The repetition is very emphatic, and is added for the purpose of confirming the statement; for when our affairs are desperate, we think that we are ruined, but at that very time we ought especially to hope, because the Lord generally selects it for giving a display of his power. For this reason, by extolling his loftiness, he arouses believers to the exercise of courage, that they may boldly defy the insolence of their enemies. [1]

Footnotes

1 - "The emphasis is not upon the pronoun (Barnes), which in that case would have been expressed in Hebrew, but upon the adverb now, which is twice repeated to imply that the time for the divine interposition is arrived, and that there shall be no more delay." -- Alexander.

Now - This verse commences another transition. In the previous verses, the desolation of the land had been described, and the hopelessness of obtaining any terms of favor from Sennacherib, or of binding him to any compact, bad been stated. In this state of things, when inevitable ruin seemed to be coming upon the nation, God said that he would interpose.
Will I rise - To vengeance; or to punish the invading host. The emphasis in this passage should be placed on 'I,' indicating that Yahweh would himself do what could not be effected by people.
Now will I be exalted - That is, God would so interpose that it should be manifest that it was his hand that brought deliverance.

Now will I (p) rise, saith the LORD; now will I be exalted; now will I lift up myself.
(p) To help and deliver my Church.

Now will I rise, saith the Lord,.... At the last extremity, when things are come to a crisis; his interest at the lowest, and the kingdom of antichrist at its highest pitch; the whore of Rome triumphing over the slain witnesses, and boasting she was a queen, and knew no sorrow: this will be God's fit time to exert himself, and get him honour and glory: he before was as one lain down and asleep, as if quite negligent and careless about his honour and interest; but now he determines to arise, and show himself strong on the behalf of it; see Psalm 12:5,
now will I be exalted; that is, in his power, by the destruction of the enemies of his church; and in the hearts and mouths of his people, on account of their deliverance and salvation:
now will I lift up myself; show himself above his enemies, higher and greater than they, and reduce them to a low estate and condition. The repetition of the word "now" has its emphasis; and is designed to observe the time of God's appearing in the cause of his people, and the fitness and propriety of it; and to quicken their attention to it, as well as to express the certainty of it, and the firmness of his resolution to do it without delay, and the vehemence and ardour with which he would set about it.

The sight of His people's misery arouses Jehovah; He has let the enemy go far enough.
I--emphatic; God Himself will do what man could not.