Passivation means the formation of a protective passive layer. It makes little difference here whether this is done in natural way by moisture and oxygen (within several days) or by passivating chemicals (within minutes).
However, since there is still a risk of corrosion until the passive layer has been fully formed, it is recommended that the passivation is done by chemical means. Passivation can only be done on metallically clean surfaces.
This means that passivation is always the second step after a pickling process unless you can be sure that no unwanted (ferritic) deposits got onto the surface during production.