The phrase "was source strength" can be expressed in various synonymous forms. For instance, "originated power" or "derived energy" are good alternatives. Other options include "started force", "emerged vigour", "stemmed potency", and "spawned might". Each of these synonyms carries a slightly different nuance, but overall they convey the same idea of originating or generating power or strength. By using different synonyms for a phrase or word, a writer can lend diversity and depth to their writing style, creating a more engaging and sophisticated text that keeps a reader's attention.