Actually, this is quite easy to understand, especially if you take slightly bigger excerpt from Chapter 4 like bellow.
As usual in his works, Nietzsche is fighting against spirit of content, seeking of peace, slave mentality, priestly morality of obeying (monk morality), modesty, humility . It is well known that Nietzsche was seeking road to Übermensch. For Nietzsche (and for Übermensch) life was a struggle to improve himself and gain more power (Will to power).
Therefore, for Nietzsche, happiness was not to have easy life, life without struggle ("Everything now turns out best for me") and to stoically accept and be content with anything ("I now love every fate"). Instead, happiness was to have passion and strength to meet life's obstacles and overcome them, thus becoming better. It is compatible with his famous maxim What does not kill me makes me stronger.
THE DISAPPOINTED ONE SPEAKS--"I listened for the echo and I heard only praise".
We all feign to ourselves that we are simpler than we are, we thus relax ourselves away from our fellows.
A discerning one might easily regard himself at present as the animalization of God.
Discovering reciprocal love should really disenchant the lover with regard to the beloved. "What! She is modest enough to love even you? Or stupid enough? Or--or---"
THE DANGER IN HAPPINESS.--"Everything now turns out best for me, I now love every fate:--who would like to be my fate?"
Not their love of humanity, but the impotence of their love, prevents the Christians of today--burning us.
The pia fraus is still more repugnant to the taste (the "piety") of the free spirit (the "pious man of knowledge") than the impia fraus. Hence the profound lack of judgment, in comparison with the Church, characteristic of the type "free spirit"--as ITS non-freedom.