  Using SU(3) lattice QCD, we investigate role of spatial gluons for hadron
masses in the Coulomb gauge, considering the relation between QCD and the quark
model. From the Coulomb-gauge configurations at the quenched level on a $16^3
\times 32$ lattice at $\beta$ = 6.0, we consider the $\vec{A} = 0$ projection,
where all the spatial gluon fields are set to zero. In this projection, the
inter-quark potential is unchanged. We investigate light hadron masses and find
that nucleon and delta baryon masses are almost degenerate. This result
suggests that the N-$\Delta$ mass difference arises from the color-magnetic
interactions, which is consistent with the quark model picture. Next, as a
generalization of this projection, we expand spatial gluon fields in terms of
Faddeev-Popov eigenmodes and leave only some partial components. We find that
the ${\rm N}-\Delta$ and $0^{++}-2^{++}$ glueball mass splittings are almost
reproduced only with 1 \% low-lying components. This suggests that low-lying
color-magnetic interaction leads to the hadron mass splitting.
