Anchors achieve holding power either by "hooking" into the seabed, or via sheer mass, or a combination of the two. I love the anchor as a symbol. This is covered more in Hope is an Anchor part 2.
When speaking about an anchor, being "hooked" to the seabed has reference to being sealed and bound to God by covenant. Christ descended below all things, making it possible for him to be in and through all things. He has the knowledge of how to reconcile all to the Father. Thus, to be anchored to anything or anyone else is foolish.
One of my favorite hymns also speaks of more sea symbols Many of these have lead my mind to a place of peace. The hymn is Brightly Beams our Fathers Mercy. A lighthouse, a ship, the sea, and rays of hope to all struggling or fainting seamen. Here's a pretty good audio of the hymn.
From his lighthouse evermore,
But to us he gives the keeping
Of the lights along the shore.
Let the lower lights be burning;
Send a gleam across the wave.
Some poor fainting, struggling seaman
You may rescue, you may save.
Dark the night of sin has settled;
Loud the angry billows roar.
Eager eyes are watching, longing,
For the lights along the shore.
Trim your feeble lamp, my brother;
Some poor sailor, tempest-tossed,
Trying now to make the harbor,
In the darkness may be lost.