Going "straight to the horse's mouth" <--- idiom, it turns out that Trine's book is available at Project Gutenberg. I don't know if this is exactly the same thing that the author of your passage means by it, but this is how Trine describes it. It means something like "God, as I choose to understand and experience God." http://www.gutenberg.org/cache/epub/23559/pg23559-images.html 1) As one comes into and lives continually in the full, conscious realization of his oneness with the Infinite Life and Power, then all else follows. This it is that brings the realization of such splendors, and beauties, and joys as a life that is thus related with the Infinite Power alone can know. This it is to come into the realization of heaven's richest treasures while walking the earth. This it is to bring heaven down to earth, or rather to bring earth up to heaven. This it is to exchange weakness and impotence for strength; sorrows and sighings for joy; fears and forebodings for faith; longings for realizations. This it is to come into fullness of peace, power, and plenty. This it is to be in tune with the Infinite. 2) The great central fact of the universe is that Spirit of Infinite Life and Power that is behind all, that animates all, that manifests itself in and through all; that self-existent principle of life from which all has come, and not only from which all has come, but from which all is continually coming... ...This Spirit of Infinite Life and Power that is behind all is what I call God. I care not what term you may use, be it Kindly Light, Providence, the Over Soul, Omnipotence, or whatever term may be most convenient. I care not what the term may be as long as we are agreed in regard to the great central fact itself. God, then, is this Infinite Spirit which fills all the universe with Himself alone, so that all is from Him and in Him, and there is nothing that is outside.

It isn't very well-defined. "The infinite" is probably a way to _avoid_ specifying God; it is the kind of language that might be used by deists or pantheists or spiritualists. It means something like "the universe" or "the cosmos" or the "the unknowable." To be "in tune with the infinite" means to have some enhanced feeling of connection or understanding of some kind of ultimate reality beyond what we know with the senses. Actually, on doing an Internet search, I find that "in tune with the Infinite" is associated with something called the New Thought Movement, that "In Tune with the Infinite" is the title of an 1897 book by Ralph Waldo Trine, and that the "Chicken Soup for the Soul" series (from which your quotation comes) does have some connection to the New Thought Movement. In the United States, where there is no state religion and a great deal of religious diversity, people writing about spiritual matters sometimes use language like that so that they can connect with a wide audience without offending anyone by being too specific about religion. I haven't read the book but I get the impression that "Chicken Soup for the Soul" may be advocating a greater emphasis on _spirituality in general._

You're welcome. But I don't feel I'm helping you very much, unfortunately.

Thank you very much, Mikkel.

OK, I see. Well, poor you. The “infinite” must be some kind of spiritual realm or power. “Being in tune with something” means to understand or agree with something. So perhaps it means something like “If I had better understood the spiritual reality”. Cambridge Dictionary: If you are in tune with people or ideas, you understand or agree with them, and if you are out of tune with them, you do not: “Much of his success comes from being in tune with what his customers want.” “Her theories were out of tune with the scientific thinking of the time.”