Does the statement of Moses (peace be upon him): "It is none but Your trial by which You cause to stray whom You will and guide whom You will" cause embarrassment, and how can this ambiguity be removed?

The Almighty Allah's saying, quoting His Prophet Moses (peace be upon him): "It is none but Your trial by which You cause to err whom You will and guide whom You will" is part of verse (155) from Surat Al-A'raf.

"Fitnah" (trial) here means testing and tribulation, and Moses understood this from Allah's saying to him: "for indeed We have tried your people after you."

The phrase: "You cause to err whom You will and guide whom You will" emphasizes Allah's absolute power in guidance and misguidance, as mentioned in other verses like: "So whoever Allah intends to guide - He expands his breast to Islam; and whoever He intends to misguide - He makes his breast tight and constricted."