THE expression is referred to in one of the passages in the first letter of St. Peter. The complete passage says: As obedient children, do not conform to the passions of your former ignorance (1,14)
Of course, as human persons, we always have some passions. These are strong emotions that drive us to action. They are a result of a combination of thingsgenes, a sensation of an inner need that seeks to be satisfied, etc.
We just have to make sure that while our passions can have their own constitution peculiar to each individual, they just cannot be left at their biological level. Otherwise, our passions would be akin to the passions of any animal that is by nature irrational, following a logic that is completely shaped by instincts alone and nothing beyond.
Like anything else in human life, our passions also need to be educated, grounded and oriented to what is truly proper to us. They should not just be a product of our genes and hormones and the other chemicals and elements that come into play. They have to be under the supervision of our reason and ultimately of our faith, hope and charity.
Thus, depending on how they are educated, they can either be good passions or bad. Yes, we should try to be passionate in our life, because that is what is ideal for us. But lets make sure that our passions are the good ones, those that are properly inspired and directed, and that truly express our dignity as persons and ultimately as children of God, image and likeness of his.
The passions of ignorance refer to those that do not spring from our knowing and loving relation with God. They are more like the passions of the animals, except that they are fueled not only by instincts, which are what fuel animal passions, but also by the powers of our intelligence and will that go beyond what our instincts can dictate. And these powers of our intelligence and will are not inspired by faith, hope and charity.
To avoid falling into this kind of passions, we have to see to it that we inspire them with the spirit of God, which is one of love, compassion and everything else that God has shown us through Christ in the Holy Spirit.
In other words, our passions should not just be purely human passions which, as described in many instances in the Bible, are lusts of our flesh, fulfilling the desires of the flesh and of the mind. (Eph 2,3)
Again in that first letter of St. Peter, we are told about what these passions of ignorance were: For you have spent enough time in the past carrying out the same desires as the Gentiles: living in debauchery, lust, drunkenness, orgies, carousing and detestable idolatry (4.3)
Our passions should be divinized. They should aim at nothing less than holiness, just like what St. Peter again said in his first letter: But just as he who called you is holy, so be holy in all you do, for it is written, Be holy, because I am holy. (1,15)
We really need to check if the passions we have are the right ones. At the moment, it can be clearly seen that most of the passions many people show nowadays are spent on self-seeking and self-absorption. They are not oriented toward God, toward sanctification.
There is also that wrong belief that being passionate about God will compromise our humanity. Hardly anything can be farther from the truth. Being with God, in fact, perfects and completes our humanity. Without God, our Creator and heaven, we are nothing, or at best, we would turn out to be like any animal in human form. Yes, we would look and behave like humans, but we really are not if we are not with God!