Decreasing the resistance in the input circuit of a transistor and its effect on the output current and voltage
I will divide the answer into two parts: 

1) (r=(ΔVBEΔIB)) is the formula for dynamic resistance when the input is A.C. Here you should apply the KVL. (Vbb – IB Rb = 0.7). Thus, decreasing the value of R will increase (Ib). And if the transistor is in active region, Ic will be proportional to Ib and hence the bulb will glow brighter.

2) If you keep on decreasing the value of R, transistor will enter into saturation. I am guessing the book means to say saturation by using the term more forward biased. Because in saturation, (VCE) = 0.2V.