In Tune with the Infinite opens with a prelude contrasting the optimist and the pessimist, each building a world from within according to his point of view. From there Trine sets out his governing claim: the great central fact of the universe is a Spirit of Infinite Life and Power that is behind all, animates all, and is the source from which everything continually comes.
Human beings, on this view, are individualized expressions of that one Life. They differ from it in degree, not in essence, as a drop of water shares the nature of the ocean it was taken from. Trine illustrates this with a mountain reservoir feeding a smaller one in the valley: the supply flows in, yet the water is identical in kind. The only real limitations a person has, he argues, are those they set for themselves through not knowing their own nature.
The book then names the supreme fact of human life: a conscious, vital realization of one's oneness with the Infinite, and the full opening of oneself to its divine inflow. Most people keep themselves closed through ignorance; the prophets, seers, and sages were simply those who opened most completely. Trine presents thought as the channel for this opening, and as a creative and magnetic force in its own right, since like attracts like across a vast ocean of shared thought.
Successive chapters apply the principle to particular goods: bodily health and vigor, the power of love, wisdom and interior illumination, perfect peace, fullness of power, and plenty. The pattern is consistent. The desired condition already exists in the Infinite source; the work is inward, holding the right thought and attitude so the inflow can bring health, calm, and prosperity into expression. Peace, Trine insists, lies not in the external world but within one's own soul.
The closing chapters universalize the teaching. Trine argues that the same truth runs through all religions, that people quarrel over trifles but agree on the great fundamentals, and that coming into tune with the Infinite is how anyone may grow toward the stature of the world's prophets and saviours. The book ends by inviting the reader to enter now into the realization of these highest riches.