‘Return, O YHWH, deliver my soul,
Save me for your lovingkindness' sake,
For in death there is no remembrance of you,
In Sheol who will give you thanks?'
He senses the loss of YHWH's presence (compare Psalms 51:11). He feels that his sins have separated between him and God. So he pleads for Him to come back to him, on the basis of His warm covenant love, His lovingkindness, so as to heal him and restore their relationship. For he points out that he cannot worship YHWH if he dies and goes to the grave.
Sheol means the mysterious grave world where the dead go, and where they are only shadows without real life, in the land of silence and forgetfulness from where no man could return (Psalms 30:9; Psalms 88:10-12; Psalms 115:17; Isaiah 14:9; Ezekiel 31:17; Ezekiel 32; Job 3:17). And he felt so miserable and sinful, that unlike some other psalmists he could not muster up the thought that he might go to be with God (contrast Psalms 16:10-11; Psalms 23:6; Psalms 49:15; Psalms 73:24-25; Psalms 139:24).