Psalm 31:10

For my life is spent with grief, and my years with sighing,
&c.] Which shows the continuance of his troubles, and that his whole life had been, as it were, an uninterrupted series of sorrows;

my strength faileth because of mine iniquity;
this opens the source and spring of all his grief and trouble; his sin, and the sin of his nature, in which he was conceived and born; indwelling sin, which remained and worked in him; and it may be also the sin of unbelief, which beset him, and prevailed in him, notwithstanding the instances of divine goodness, the declarations of grace, the discoveries of love, and the exceeding great and precious promises he had made to him; as also his daily sins and infirmities, and very likely some great backslidings, which had brought grief of soul upon aim, and which grief affected the several parts of his body. Sin was the cause of the failure of natural strength in Adam and his posterity; of diseases and death, by which their strength is weakened in the way; and was the cause of impairing moral strength in men to do that which is good, and has a very great influence on the spiritual strength of the Lord's people, in the exercise of grace;

and my bones are consumed;
which are the firmest and strongest parts of the human body, and the support of it.