The correct spelling of the phrase "wert source of strength" is actually "worth source of strength." This confusion may arise from the fact that the pronunciation of "worth" can sound like "wert" to some people. In IPA phonetic transcription, "worth" is pronounced as /wərθ/, with the "th" representing the voiceless dental fricative sound. So, whenever you come across the phrase "wert source of strength" in your reading, remember that the correct spelling is "worth source of strength."