“the Father himself loves you for loving me, and believing that I came from God.” I may say to Ellie “I love you because you make these fabulous meals”, but she knows full well that that isn’t the only or even the primary reason I love her. If Jesus should have said such a thing, it was meant in the same partial way that I meant the above.
Elsewhere and often Jesus made it very clear that God loves us unconditionally, and not because of any particular belief that we may have.
This passage reminds me of the hardshell preacher who says “Unless you confess that the Lord Jesus Christ is your personal saviour, you are going to hell.” John, or the translator of John, is speaking hardshell here and not being true to the spirit of Christ as I know it.
God loves all mankind– unconditionally. He wants us to be happy and to love one another. That was the primary message that Jesus brought to us from the Father.
“Jesus answered them: Do you believe at last?” His use of ‘believe’ here indicates rather plainly in the context that he is not talking about subscribing to an intellectual proposition but about trust, commitment, integrity, all of which he understood that they would soon betray.