These ideas were a combination of Neo-Platonism, Swedenbourgian mysticism, Romanticism, German Idealistic philosophy, reaction against Empiricism a la Hume, New England Puritanism and a dash of personal genius. For Emerson, transcendentalism was Idealism for 1842. If I may add, it was Idealism for Emerson in 1842. At its base, transcendentalism is certainly on the idealistic side of the great divide between idealism and realism. There is an ideal world that coexists with the real world, a world of noumena and a world of phenomena.
Nature parallels the individual mind.
The natural, sensual world of phenomena is a representation by which we may better comprehend the world of noumena. God is energy, a force, not a particular separate being. God breathes through nature and man attempts to open himself up to this influx. Nothing is static. The greatest goal is to achieve the transcendental moment, the moment when one is open to the to and fro flow of the influx.