The Big Book presents everything up to the prayer on page 63 as ideas for me to take in. Mental processes are activities, and involve physical actions too: sitting, maybe listening, reading, thinking (for which I employ my physical brain), discussing, and possibly writing (because that can help organise disordered thoughts and sift the important from the unimportant).
Working With Others sets out how to work with a newcomer, and the descriptions are descriptions of actions: mostly reading (the newcomer being encouraged to read the Book) and discussion. These are actions too.
However, there is validity to the idea there is a substantive change at Step Four: everything up to the first actions of Step Four represents, as it were, 'preparation for the trip'; Step Four onwards represents 'taking the trip'.
Whilst the first three Steps involve action of a sort, they will not have any permanent effect unless implemented in the form of the later Steps. Step Three, as a decision, contains the seeds of the remaining nine Steps. Those seeds need to be planted and grow.