You are asking about Psalm 103, verses 1-5:
Bless the Lord, O my soul; and all that is within me;
bless his holy name!
Bless the Lord, O my soul, and forget not all his benefits,
who forgives all your iniquity, who heals all your diseases,
who redeems your life from the Pit,
who crowns you with steadfast love and mercy,
who satisfies you with good as long as you live,
so that your youth is renewed like the eagle's.
It's beautiful, isn't it? This Psalm is generally considered to be a song of thanksgiving for a recovery from disease—and I think you can feel in these words the sense of relief and appreciation we all experience when we suddenly feel healthier and more hopeful after a bout of illness. When we understand the Lord to be the Christ, the Presence and Power of God that is our true identity, we feel a sense of gratitude for a Source that entrusts us with infinite possibilities for love and healing.
It is the Christ within that dissolves our sense of guilt and iniquity. It is the energy of the Christ that heals every expression of false belief in limitation and disease. It is Christ awareness that lifts us out of the Pit of depression and doom that can express out of false beliefs that we are somehow separate from our infinite Source.
Jesus taught that we must become as children—regain the simple awareness of infinite Love and constant support—in order to achieve and express the new consciousness that is the kingdom of heaven. It is in that sense that surrendering to our indwelling Christ allows our youth to be renewed.