In the Summa theologiae, Ia-IIae, q. 68, a. 2, Saint Thomas Aquinas basically says we are too stupid.  Even with the virtues of faith, hope, and charity, we’d be stupid enough to damn ourselves if the Holy Spirit did not add over and above this, not only virtues, but dispositions for a way of acting in regards to a Person (the Holy Spirit).

He says the Gifts of the Holy Spirit are necessary for salvation.

If they’re necessary for salvation, how much more necessary they must be for the contemplative life!

The contemplative Gifts are Wisdom, Understanding, and Knowledge. The active Gifts are Counsel, Piety, Fortitude, and Fear of God. All are necessary for everyone. Depending on what tune the Holy Spirit is playing in our lives, he will play in a key that emphasizes those Gifts more. Each tune is unique. Many are in an active key. Some are in a contemplative key.

It’s sort of like being a technically skilled or virtuous dancer (having the theological virtues of faith, hope, and charity) but needing an experiential relationship to your specific partner (the seven Gifts) to make the dance really go all the way home. At least, that’s how I think of it. But as we know, I’m human and a bit stupid. ^^