Lanthanoid have similar chemical and physical properties. Why?

All the lanthanides have similar outer electronic confugration and exibit common +3 Oxidation state in their compounds, therefore lanthanides have exceedingly similar chemical properties. Their similarity is much closer than that of ordinary transition elements because lanthanides differ mainly in the number of 4f electrons which are buried deep in the atoms of lanthanides and thus don’t influence their properties. Moreover due to lanthanide contraction there is very small difference in the size of these ions is almost identical which results in similar chemical properties of these elements.