They are widening themselves through their connection, through the processes that run in each one of them (and them as one, simultaneously) as they experience their “together". One helps the other to “increase" whichever of these two(heart, thinking) each one “uses less”. The soul calls them to their unification. For both of them to be led to the construction of this bridge, and be fully in touch with their soul.
Of course, this is one of the things they do. The widening to the Self’s extend includes more stages, but also more processes that run in parallel with the present phase.
In fiction, of course…