This is a metaphor and not a simile. The brief reason is because it does not contain the word "as" or the word "like." If it were a simile, it would say "Love is like an anchor for the soul."
Both a metaphor and a simile compare one thing to another. In this case, love is being compared to an anchor. Presumably, love is supposed to keep a soul safe and make it stay in the right place just like an anchor does. But a metaphor does this directly. In this case, it says "love is." If it were a simile, it would say "love is like."
So both figures of speech are doing more or less the same thing, but one does it directly (simile) and the other does it indirectly.
IT IS METAPHOR BECAUSE LOVE IS COMPARED WITH THE ANCHOR OF SOUL.