Hearken unto the voice of my cry - My cry for assistance. The word "voice" refers to the utterance of his desires, or to his "expressed" wishes in a time of trouble.
My King, and my God - Though he was himself a king, yet he acknowledged his subjection to God as his supreme Ruler, and looked up to Him to protect him in his dangers, and to restore him to his rights. He was, at the same time, his God - his covenant God - to whom he felt that he was permitted to come in the hour of trouble, and whose blessing he was permitted to invoke.
For unto thee will I pray - He had no one else to go to in his troubles, and he felt that he "might" approach the living God. It was his fixed purpose - his regular habit - to pray to him, and to seek his favor and friendship, and he felt that he was permitted to do so now.

Hearken unto the voice of my cry - We may easily find the process through which David's mind was now passing:
1. We have seen from the preceding Psalm that he lay down in a very happy frame of mind, and that he had enjoyed profound repose.
2. As soon as he awakes in the morning, his heart, having a right direction, resumes its work.
3. He meditates on God's goodness; and on his own happy state, though pursued by enemies, and only safe as long as God preserved him by an almighty hand and especial providence.
4. This shows him the need he has of the continual protection of the Most High; and therefore he begins to form his meditation and the desires of his heart into words, to which he entreats the Lord to give ear.
5. As he was accustomed to have answers to his prayers, he feels the necessity of being importunate! and therefore lifts up his voice.
6. Seeing the workers of iniquity, liars, and blood-thirsty men strong to accomplish their own purposes in the destruction of the godly, he becomes greatly in earnest, and cries unto the Lord: "Hearken unto the voice of my cry."
7. He knows that, in order to have a right answer, he must have a proper disposition of mind. He feels his subjection to the supreme authority of the Most High, and is ready to do his will and obey his laws; therefore he prays to God as his lying: "Hearken, my King and my God." I have not only taken thee for my God, to save, defend, and make me happy; but I have taken thee for my King, to govern, direct, and rule over me.
8. Knowing the necessity and success of prayer, he purposes to continue in the spirit and practice of it: "Unto thee will I pray." R. S. Jarchi gives this a pretty and pious turn: "When I have power to pray, and to ask for the things I need, then, O Lord, give ear to my words; but when I have no power to plead with thee, and fear seizes on my heart, then, O Lord, consider my meditation!"

Hearken unto the voice of my cry,.... Which seems to intend more than groans or words, even a loud outcry, as of a person in great distress; such as the strong crying of Christ, in the days of his flesh, when on the cross, forsaken by God, deserted by his friends, and surrounded by his enemies, Hebrews 5:7; and such, in some measure, was the case of David. The arguments used by him, that the Lord would hearken to him, are as follow: and the first is taken from his interest in the Lord, and his relation to him,
my King and my God; the Lord was David's King in a civil sense; though David was a king over others, yet the Lord, who is the King of kings, was King over him, and he owned him to be so; he was set upon the throne by him, had his kingdom from him, and was accountable to him: and he was his King in a natural sense, the kingdom of nature and providence belonging to him, as he was his Creator, preserver, protector, and defender; and in a spiritual sense, he being delivered from the dominion of other lords, sin, Satan, and the world, and brought to a subjection to him by his Spirit and grace; and so to own him as his King and Lawgiver, as well as his Saviour. And he was his God; not in a general way, as he is the God of the spirits of all flesh living; nor merely in the peculiar way in which he was the God of the people of Israel; but in a most special manner, as being his covenant God and Father in Christ. He was his God, not only as the God of nature and providence, but as the God of all grace; who had distinguished him by special and spiritual blessings and favours; and whom David loved, believed in, and worshipped as his God. And this his interest in him, and relation to him, he uses with great pertinence and propriety, as an argument that he might be heard by him; since the Lord was his King, and he his subject; the Lord was his God, and he one of his people; the Lord was his father, and he a child of his; and therefore entreats and hopes to be heard; see Isaiah 63:15. His next argument is taken from his resolution to pray to him, and to continue to do so:
for unto thee will I pray; and only to thee: not to the gods of the Heathen, to idols, the works of men's hands, who can neither hear nor save: and to thee always; suggesting, that he would never leave off praying till he was heard; he would give him no rest, day nor night, until he received an answer.

Hearken--incline the ear (Psalm 10:17; compare Psalm 61:2) --give close attention.
my cry--that is, for help (Psalm 61:2; Jeremiah 8:19).
my King--thus by covenant relation interested in my cause.