The introductory letter to the dating
The second -- or sometimes third line -- reinforces and extends the meaning of the first, like a second wave that mounts higher than the first, and a third even higher yet (for example, Psalms 92:9; 93:3; 1).When interpreting Hebrew poetry however, it's important not to overemphasize the nuances between the similar words, for example, between "man" and "Son of man" in 8:4 or "my soul" and "my flesh" in Psalm 63:1.
Simile is a comparison which is made explicit by the presence of the word "like" or "as." For example: A metaphor communicates a more vivid image than a simile because it is implicit and draws the comparison more closely.
As you study the Psalms, be aware of the images that are used and the thoughts and emotions that they are intended to evoke in us, the readers.
The Psalms are meant to be sung -- and accompanied by musical instruments.
David, the author of many of the psalms, was a skilled player of the "harp," more accurately perhaps, the "lyre" ( In western poetry we use both rhyme and rhythm in traditional poems.
Imagery has a way of fixing an idea in our minds with clarity. In prose we might say with some accuracy: "God meets all our needs and protects us." It is true, but not particularly memorable.