The intellect and the will are part of our soul. The soul does not "hold" the emotions. The intellect and will, therefore, must be formed in order for us to become saints. We are inclined to be good or bad according to grace and according to the intellect and will.
We know that certain things are good. It is human to be able to understand good and evil. It is human to make moral decisions. We are more free to make moral decisions if our intellect and wills are in conformity with Christ and His Church.
If we are, as we believe, made in the image and likeness of God, then we are made to be rational, to form our wills and intellects in the Mind of Christ, which is revealed in the Mind of the Church.
If an adult is not working on the rational, unless there is a natural inability to do so, this could be a sin. Most people who do not pursue knowledge fall into the sin of sloth. Another reason could be pride, as one may not want to know one is sinning, one is choosing evil.
If one is running away from God, then one may ignore the intellect. One must seek God and the good.
Another reason why people may not pursue being a rational Catholic could be that one is steeped in heresy, particularly the Protestants one of sola fide, sola Scriptura, sola Christus, sola gratia.
Sadly, many of the Charismatics fall into these errors. And, in doing so, concentrate on experiences rather than the intellect.
I can write about this subject because I have read some of the greatest writers given to the Church: St. Thomas Aquinas, the Popes in the 19th, 20th, 21st centuries. Both Blessed John Paul II and the Pope Emeritus reminded us of the overlap of Faith and Reason. All Catholics have access to the texts which help us think, and approach our Faith in a reasonable manner.
The saint comes to a unity of the mind, the heart, the intellect. That unity is our goal in seeking perfection.
There must be purity in all three faculties. The conscience must be formed. Most likely, we are culpable for not forming our consciences. Conscience is more than merely making a decision. It is making a right decision.
AND THAT IS OUR RESPONSIBILITY.