Have mercy upon me, O Lord, for I am in trouble - The nature and sources of his trouble are specified in the verses following. He seems to have regarded all his trouble as the result of sin, either the sin of his heart, of which he alone was conscious, or of some open act of sin, that had been the means of bringing this affliction upon him, Psalms 31:10. As a consequence of this, he says that he was subjected to the reproach of his enemies, and shunned by his neighbors and his acquaintances; that he was forgotten by them like a dead man out of mind; that he was exposed to the slander of others, and that they conspired against his life, Psalms 31:11-13. In view of all this he calls earnestly upon God to save him in his troubles, and to be his helper and friend.
Mine eye is consumed with grief - That is, with weeping. See the notes at Psalms 6:7.
Yea, my soul - That is, my spirit, my life, my mind. My powers are weakened and exhausted by excessive grief.
And my belly - My bowels: regarded as the seat of the affections. See the notes at Isaiah 16:11; compare Psalms 22:14. The effect of his grief was to exhaust his strength, and to make his heart sink within him.