The second בִּנְיָן we are going to study in this series about Hebrew verbs is the פִּיעֶל. This category usually include verbs whose meaning is somehow more intense than the “simple” פָּעַל verb.
לִכְתֹּב – to write
לְכַתֵּב – to address
This way, we can see that לִכְתֹּב refers to writing in a broader sense, whereas לְכַתֵּב refers to writing a specific thing, “an address”, thus being more intense.