Psalm 139 is about God's omnipresence and omniscience – that God is everywhere and knows everything about us. Verse 9, "If I take the wings of the dawn, and settle in the uttermost parts of the sea," emphasizes the vastness of God's reach and the futility of trying to escape Him. Let's break it down:

"If I take the wings of the dawn..." This is a poetic expression for traveling as fast as the dawn itself. Dawn spreads rapidly across the sky, so "wings of the dawn" symbolizes extreme speed and distance. It implies a journey to the farthest east, where the dawn breaks.

"...and settle in the uttermost parts of the sea;" This refers to the most distant, remote, and deepest parts of the ocean. It represents the farthest west.

The combined meaning is:

The verse essentially says, "Even if I could travel as fast as the dawn and reach the most distant point in the sea, I still wouldn't be able to escape God's presence." No matter how far or how fast the Psalmist travels, God is already there. It is a figurative way of expressing the impossibility of escaping God's all-encompassing presence.

In summary, the verse means:

God is everywhere: There is no place one can go to be hidden from God.
God's presence is inescapable: No matter how hard one tries to flee, God is already there.
The verse highlights God's omnipresence: It's a powerful statement about the vastness and pervasiveness of God's presence in the world.
Impossibility to Hide: It is impossible to hide from God or escape His knowledge and care.