However, when He, the Spirit of truth, has come, He will guide you into all truth; for He will not speak on His own authority, but whatever He hears He will speak; and He will tell you things to come. --John 16:13, NKJV
When we consider the source of truth, we must begin with "He," the Spirit of Truth whose characteristic nature is truth. "He will Guide you"--suggesting a hand to lead in graciousness and gentleness and the "gradual-ness" of His teaching. Note the completeness of the truth into which the Spirit guides. "Into all truth" is the assurance of gradual and growing acquaintance with the spiritual truth which is revealed as we grow. Never can mortals learn all the truths that the Spirit has to teach; but as one is true to His guidance, He will reveal new truths.