The Fifth Gift of the Holy Spirit:
Knowledge is the fifth of the seven gifts of the Holy Spirit enumerated in Isaiah 11:2-3. They are present in their fullness in Jesus Christ, Whom Isaiah foretold (Isaiah 11:1), but they are available to all Christians who are in a state of grace. We receive the gifts of the Holy Spirit when we are infused with sanctifying grace—when, for example, we receive a sacrament worthily. As the Catechism of the Catholic Church notes, "They complete and perfect the virtues of those who receive them." When we are infused with the gifts of the Holy Spirit, we respond to the promptings of the Holy Spirit as if by instinct.
The Perfection of Faith:
Like wisdom, knowledge perfects the theological virtue of faith. The aims of knowledge and wisdom are different, however. Whereas wisdom helps us to penetrate divine truth and prepares us to judge all things according to that truth, knowledge gives us that ability to judge. As Fr. John A. Hardon, S.J., writes in his Modern Catholic Dictionary, "The object of this gift is the whole spectrum of created things insofar as they lead one to God."
The Application of Knowledge:
Knowledge allows us to see the circumstances of our life as God sees them, albeit in a more limited way, since we are limited by our human nature. Through the exercise of knowledge, we can ascertain God's purpose in our lives and His reason for placing us in our particular circumstances. As Father Hardon notes, knowledge is sometimes called "the science of the saints," because "it enables those who have the gift to discern easily and effectively between the impulses of temptation and the inspirations of grace." Judging all things in the light of divine truth, we can more easily distinguish between the promptings of God and the subtle wiles of the devil.