Why did Jesus quote the Shema, but not the "Athanasian Creed"?

"Yeshua answered, 'The greatest is, 'Hear, Yisra'el, the Lord our God, the Lord is one.'" -- Mark 12:29, Hebrew Names Version "The Father is God, the Son is God, and the Holy Spirit is God; and yet they are not three Gods, but one God." -- Athanasian Creed Yes, I know... show more "Yeshua answered, 'The greatest is, 'Hear, Yisra'el, the Lord our God, the Lord is one.'" -- Mark 12:29, Hebrew Names Version

"The Father is God, the Son is God, and the Holy Spirit is God; and yet they are not three Gods, but one God." -- Athanasian Creed

Yes, I know Athanasius came after Christ. I am talking about the spirit or formula of the Creed. That's why I put "Athanasian Creed" in quotation marks.
Update: @Mary: No, I am asking why Jesus acknowledged that God is One, rather than professing God as three-in-one.
Update 2: @Donny: Jesus did not say "I and the Father are one GOD." That's how it's interpreted, but that's not what Jesus said.
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