$$\require{cancel}$$
It follows from equation 1.5.3 and the definition of electric field intensity that the electric field at a distance $$r$$ from a point charge $$Q$$ is of magnitude
$\tag{1.6.2}E=\frac{Q}{4\pi\epsilon_0 r^2}.$
$\textbf{E}=\frac{Q}{4\pi\epsilon_0 r^2}\hat{\textbf{r}}=\frac{Q}{4\pi \epsilon_0 r^3}\textbf{r}.\tag{1.6.3}$
Here $$\hat{\textbf{r}}$$ is a unit vector in the radial direction, and $$\textbf{r}$$ is a vector of length $$r$$ in the radial direction.