What is spirituality? It is often a loose term, whose use justifies a lot of nonsense. Christians, however, have always had a good idea of what could be meant by “spirituality,” even where the word itself was absent. That is because Christians have a very definite idea of what the difference is between the Spirit and spirits. This is perhaps more important for us to recognize than past generations, because one of the effects of secularism is the loss of the sense of “true” and “false,” to the benefit of the “personally meaningful.” This distinction–between “true” and “false”–makes sense of Christian thought. One can’t make sense of the Bible without it: true and false prophets (Deut. 13:1-5); true and false gods (Ex. 12:12; Ps. 96:5; Is. 44:6-20); true and false Christs (Matt. 24:4-5); true and false religion (James 1:27); true and false spirits (1 John 4:1-6).
When Aquinas, then, comes to speak of makes a person “spiritual,” he does so by talking about the Holy Spirit. This Spirit, the true Spirit of God, separates a “spiritual” person from a merely “natural” person, or worse. These are his comments on 1 Corinthians 2:15, “The spiritual person judges all things.”
A person can be called “spiritual” in two senses. In one sense, with regard to the understanding being illuminated by the Spirit of God. For this reason, the Gloss says, “A person is spiritual who, obedient to the Holy Spirit, knows spiritual things faithfully and with the highest degree of certainty.” In another sense, with regard to the will being set aflame by the Holy Spirit. And the Gloss speaks of this sense as follows, “A spiritual life is that by which the Spirit of God has governance, guiding the soul, that is, the natural powers.” (In I Cor. 2.3.117)
Aquinas elaborates on this quite a bit in other writings, particularly in the sections of the Summa theologiae on the theological virtue of faith (2a2ae.1-16). It can put in a much more complicated way, but it can also be put much more simply: a spiritual person is that person illuminated by and set on fire by the Holy Spirit, or even more simply, a spiritual person is that person who has the Spirit of God. Anything else would be a false spirituality.