The Holy Spirit of God.
It is wrong to try to become completely spiritual whilst still in this world by, say, sitting atop a metaphorical, forty foot pole and meditating 24/7. If we could achieve a form of total spiritual isolation in some strange way then whatever spirituality is contained in this shell of flesh and blood that we inhabit would simply depart from our bodies.
Why? We would then have ceased struggling and no longer be trying, as Paul so eloquently phrased it, to win the race of Life. The metamorphosis would then cease and we would spiritually die in our earthly bodies just as a caterpillar would that tried to behave like a butterfly before the time was ripe for it to do so. As the foremost task of the caterpillar whilst alive is to work towards becoming a butterfly by doing what is essential to enable the change to be made, our most important task, is to do what is necessary during our earthly life to enable us to don our costume of immortality when we die.
The caterpillar has one advantage over human beings due to its developmental actions being instinctive, and so it will work tirelessly towards reaching its goal without the hindrance of a cognitive intellect. We, on the other hand, have a reasoning intelligence which, when combined with an acute awareness of self, makes many of us mistakenly believe that the earthly body we inhabit is the only one. We then stop struggling and growing in the spirit and sadly, like the caterpillar should it cease in its toil, we will die and our humanity will never know the splendour and glory of the next stage that is there for the taking.
All we need to do to emerge at death into the butterfly of spirituality is to love the Lord our God with all our hearts and minds and souls, and to love others as ourselves. (Matthew 22: 37-40) There is neither more nor less to it than that.
We can and must, in this life, begin the process of pulling on our spiritual clothes. The caterpillar does not suddenly grow its wings when it dies for it must begin its change while still alive and only then, if and when the process is completed, will it be able to shake off its old body and live in its new form and fly.
Just as I cannot see light itself but only those things it illuminates and makes visible I can only know God when His divine light illuminates my mind through His Holy Spirit. Whilst I cannot see God, I can truly know Him through His reflected glory which is Christ, the Incarnate Son of God, and this insight is enabled by the Holy Spirit working within me.
The living, acting God of Christian theology is, of course, the source of all my concepts and whilst this makes them true they are possibly distorted by my lifetime-acquired personal prejudices being loaded on them. Everything I do comes from God, but it is up to me to decide whether I perform my deeds like Saul or Paul, but without input from God I would have no concepts at all.
Somehow I seem, moth-like, to be moving around the periphery of enlightenment; I advance further in, only to discover that there is still far to go. Temporal reality increasingly becomes the dream which then turns into Spiritual reality. The yoke becomes both light and heavy at the same time as realisation begins to force open the door of understanding just a smidgen wider. It does not frighten me, and neither does it fascinate me, at least not within the worldly meaning of those words. I am simply going home; in God's good time I grant you, but I am going home.
The spiritual longing which consumes me, tells me that just as the hungry man is evidence of his need for food, it (the yearning and longing) is evidence that I am meant for union with our Father. The Holy Spirit of God is not some intellectual concept. It is the Mind of God, the Will of God, the Heart of God who actively participates in our lives, showing concern without being coercive.
Don't be too concerned that you are unable to place an accurate interpretation on the nature of the Holy Spirit. You have no idea why or how gravity works but you use its effects to help many aspects of your lives.
Do the same with the power of the Holy Spirit. Harness its power through prayer and marvel at just how warm you get the nearer you stand to the all embracing warmth and light of the Meridian Sun.
The Holy Spirit is the voice of our Heavenly Father, counselling, guiding, cautioning, helping and calling us back to Him and whatever it is I understand and feel about God, I now know that this knowledge and perception has been revealed to me by the Holy Spirit who, as Paul wrote in 1 Cor. 6:19 has made a temple of my body where it now resides.
Of that I have absolutely no doubt at all!