My God is the epitome of mercy and compassion (Godly type Love/charity), but not everyone is willing to humbly accept pure charity as charity and God is not going to force people to accept charity since that would make God out to be holding the shotgun at a shotgun wedding. God would know when a person will never accept His mercy (Love) and thus not choose to extend to that person further His mercy and compassion, by God's choice.
Lets look Ro. 9:
Upon leaving the shop with the Potter’s proud mark on the jar (the birth of a baby) , they are great for what they were made to do: common or special use, but after leaving the shop things can happen pleasing the Potter or embarrassing the Potter to the point He does not want His mark on the pot. So, what could happen to the pot (special or common) that would cause the Potter not to want His mark on the pot?
You have to keep in mind the context of who is writing and how Paul uses the analogy other places:
Paul uses these same Greek words: τιμὴν (honorable or special purpose) and ἀτιμίαν (dishonorable or common use) in 2 Tim. 2:20 conveying the same idea of two types of vessels in a rich person’s house, but that would mean the Paul did not use ἀτιμίαν to mean “dishonorable”, since there would not be any dishonorable vessel in a rich man’s house, so Paul’s meaning is a common used vessel.
To understand better, we have to look at:
2 Tim. 2: 20 In a large house there are articles not only of gold and silver, but also of wood and clay; some are for special purposes and some for common use. 21 Those who cleanse themselves from the latter will be instruments for special purposes, made holy, useful to the Master and prepared to do any good work.
Paul said the common (ἀτιμίαν) vessels could themselves “cleanse themselves” (their free will action) and thus become articles of honor special, holy and useful. If the vessel itself can clean up, than it is also possible the vessel can become cracked (damaged) to the point of being useless.