Albert Barnes Commentary Psalms 86:3

"Be merciful unto me, O Lord; For unto thee do I cry all the day long." — Psalms 86:3 (ASV)

Be merciful to me, O Lord - It was mercy after all that he relied on, and not justice. It was not because he had any claim on the ground that he was “holy,” but all that he had and hoped for was to be traced to the mercy of God.

For I cry to you daily - Margin, as in Hebrew, “All the day.” The meaning is, that he did this constantly, or without intermission.