The difference between the Spirit of God and the spirit of man
God created man in His image and likeness, and set him over all the other creatures on earth (Gen 1:27-28). God breathed into man the breath of life, and he became a living soul (Gen 2:7). There is much said about the differences between the spirit, soul, heart, and mind of man that has no basis in the scriptures. The Hebrew and Greek words are interchanged throughout the Bible, and are translated into English interchangeably as well. However sometimes more than one word appears in one verse seeming to make distinctions in the makeup of man (Mk 12:30, 1Thes 5:23, Heb 4:12). It is difficult if not impossible for man to make clear distinctions using proper principles of Bible study, but God can.
However, it cannot be reasonably argued by anyone who believes the Bible that God did not put a spirit in man. Even some atheistic, materialistic humanists admit there is a spiritual aspect to man, although they decline to delve much into the subject because it leads us to the Bible. The spirit of man has been called his "life force" or his "spiritual antenna". These are not inaccurate descriptions. In some ways the Spirit of God and the spirit of man are similar. Man's spirit was given him by His Creator, and therefore reflects Him in some ways (Rom 1:20). However, there are also some major differences. The Spirit of God never came into being. He always was, is, and will be (Rev 1:8). The spirit of man is not eternal that way. The spirit of man goes back to God who gave it when he dies (Ecc 3:21, Ecc 12:7). Yet that is not the big difference.
The Spirit of God is holy. That is His nature. Man is tainted by sin in his nature. Although spirit and flesh are two different things, as long as we live in these bodies we cannot completely separate the two. That is called death. The spirit of man is defiled by sin just like the flesh is (2Cor 7:1). That is actually the worst part of what sin does to us. It not only brought death to the flesh (Gen 2:17), it separates us spiritually from God who is holy (Is 59:1-2). Not only does sin damage and destroy our "life force", it damages and destroys our "spiritual antenna".
We cannot rely on our own spirit exclusively to direct us to truth and righteousness (Rom 6-8, 1Cor 1-2). We need the Holy Ghost, which is the Spirit of truth (Jn 14:17, Jn 15:26, Jn 16:13, Eph 5:9, 1Pet 1:22). Our spirits are susceptible to deception by the devil and demons, other people, and even ourselves. We can "feel" or "perceive" things with our spirits that are not necessarily in harmony with the Spirit of God. This is what false prophets have done for millennia (Deut 13:1-5). Jeremiah in particular spoke of this because it was a big problem in his day (Jer 5:31, Jer 14:14, Jer 23:22, Jer 29:9, Lam 2:14). Our own heart can make us think we are doing something good just because we sense the spiritual or religious nature of it (Num 15:39, 1Ki 12:33, Prov 28:26, Jer 9:14, Jer 23:16-26, Eze 11:21, Eze 13:17, Eze 14:5, Jam 1:26). We can even do things that are generally Christian but not the will of God for us individually. David wanted to build a temple for God. This seemed even to Nathan the prophet like a spiritual thing to do, but God told him to go back and tell David it was not His will for him to do this (2Sam 7).
It is noteworthy that the same passages that speak of our spirit being our "spiritual antenna" also warn us that they must operate in conjunction with the Spirit of God to accomplish the will of God (Rom 8, 1Cor 1-2).We need guidance to direct our spirits into the will of God. The first and foremost guide is the Bible. It was inspired by the Holy Ghost (2Tim 3:16-16, 2Pet 1:20-21). The Holy Ghost will never contradict what He has already spoken in His written word. That is confusion, and God is not the author of confusion (1Cor 14:33). Some dreams are from God, and some are from late night pizza. Another guide is spiritual authority. We all need a pastor to help us discern the will of God from our own (Heb 13:7 & 17). The Israelites went to Jeremiah to ask if it was the will of God for them to flee to Egypt (Jer 42-44). Jeremiah told them it was not, but they had already decided to do it anyway. They were not sincerely seeking the will of God. They were cursed and destroyed doing what they said was the spiritual thing to do. The same thing happened to Balaam (Num 22-24). It is true that pastors are men as we are, but God chose this office to help us (Eph 4:11-15). When we honor spiritual authority and God's system, God will honor us. When we think God has spoken to us, we can ask Him to confirm it through the scriptures and through the leadership He has given us.