John 16:13 (NKJV): "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."

In the last moments Jesus had with His disciples before His ascension, He carefully took time to tell them about the Holy Spirit Who would be the spiritual replacement for His physical presence. Up until this time, the disciples depended on being taught, guided, and led by the Son of God Whom they could physically see, hear and touch. Jesus knew He had to still their fears of being left or abandoned by Him, having to fend for themselves as believers in a fallen world. That's why he mentioned again and again that the Holy Spirit is the Spirit of truth. He can always be trusted to never mislead or misguide us. It's true that we can 'mis-hear' or misinterpret His leading, but He never makes a mistake, He is never wrong, and He is pure - His motives are never untrustworthy. This means we must continuously practice hearing His voice correctly. We find the Holy Spirit mostly leads us by the tugging or impression of our hearts, or that still, small voice from our spirits that sounds like a spontaneous thought. We must always test that voice against the Word of God. It must line up with the character, nature and principles of the Word. Another indicator is the peace we feel when we hear and follow what we feel the Lord is leading us to do. It's a peace that transcends our natural understanding because it flows from His Spirit into ours. The Bible refers to this peace as an umpire that silences the confusion and points us in the right direction. The more time we dedicate to listening to the voice of the Spirit, and practice following after His lead - we find Him to be faithful and good, and can be completely dependent on trusting Him to lead us into all truth.