By his we know that we abide in him and he in us, because he has given us his Spirit. – 1 John 4:13 ESV How do you know that you're truly saved? What gives you the rock-solid assurance that you have placed your faith in Christ and that God has accepted you as His child? John gives us one, very reliable proof: The presence of the Holy Spirit within us. “And God has given us his Spirit as proof that we live in him and he in us” (The New Living Translation). John had already talked about this matter once before back in chapter three. “Those who obey God’s commandments remain in fellowship with him, and he with them. And we know he lives in us because the Spirit he gave us lives in us” (1 John 3:24 NLT). Our very ability to obey God's commands is due to the presence of the Spirit of God within us. We would be unable to live obediently without Him. When we sinned, we would experience no conviction without His help. It is the Holy Spirit who provides us with the assurance of our salvation. Paul described Him as a kind of down-payment or guarantee of things to come. “It is God who enables us, along with you, to stand firm for Christ. He has commissioned us, and he has identified us as his own by placing the Holy Spirit in our hearts as the first installment that guarantees everything he has promised us” (2 Corinthians 1:21-22 NLT). This was a favorite theme of Paul's. He said the very same thing to the church in Ephesus. “The Spirit is God's guarantee that he will give us the inheritance he promised and that he has purchased us to be his own people. He did this so we would praise and glorify him” (Ephesians 1:14 NLT). In his letter to the believers in Rome, he added a slightly different twist: “The Spirit himself bears witness with our spirit that we are children of God” (Romans 8:16 ESV).
By THIS we know. It is the Holy Spirit within us who should provide us with an overwhelming since of peace and confidence that we belong to God. The very fact that He lives in us and is constantly attempting to guide, convict, comfort, and transform us, should let us know that God is in us and we are in God. The Holy Spirit provides us with the ability to understand the truths of God. Paul told the believers in Corinth, “we speak words given to us by the Spirit, using the Spirit’s words to explain spiritual truths” (1 Corinthians 2:13 NLT). Then he went on to explain the sad, but true facts concerning those who don't have the Spirit of God within them. “But people who aren’t spiritual can’t receive these truths from God’s Spirit. It all sounds foolish to them and they can’t understand it, for only those who are spiritual can understand what the Spirit means” (1 Corinthians 2:14 NLT). Concerning the Holy Spirit, Jesus told His disciples, “The world cannot accept him, because it neither sees him nor knows him. But you know him, for he lives with you and will be in you” (John 14:17 NET). He promised His followers that the Holy Spirit would take up residence within them. And His indwelling presence would make it possible for them to understand the words of Christ in ways they never could have before.
The Spirit provides us with assurance that we are in Christ. He lets us know that we are God's children. But it is possible to live as if He does not exist. We can treat Him as if He is not there. When we sin, we grieve Him, because we are refusing to rely upon His strength and listen to His voice in our lives. When we attempt to live the Christian life in our own strength, we quench Him. We effectively tell Him we don't need Him. And when we do, we lose all sense of assurance. We begin to doubt. We wonder why we don't seem to see any transformation in our lives. Paul saw the believers in Corinth doing the very same thing and told them, “Dear brothers and sisters, when I was with you I couldn't talk to you as I would to spiritual people. I had to talk as though you belonged to this world or as though you were infants in the Christian life” (1 Corinthians 3:1 NLT). They were not acting like Spiritual people. Yes, they had the Spirit of God within them, but they were not allowing Him to do what God had sent Him to do. They were resisting Him. They were ignoring Him. And they were living their lives as if He didn't even exist. Their lives looked more like those who who are lost and lack the Spirit altogether. Not exactly a rousing endorsement from the apostle Paul.
One of the ways we can tell if someone belongs to God is how they respond to the truth of God as found in the Word of God. When it is preached, they respond favorably. The Spirit within them either convicts or comforts them. John said that his teachings came from God and those who had the Spirit of God living in them were able to hear his words with spiritual ears. “But we belong to God, and those who know God listen to us. If they do not belong to God, they do not listen to us. That is how we know if someone has the Spirit of truth or the spirit of deception” (1 John 4:6 NLT). Spiritual people, those who have the Spirit of God living in them, are able to accept spiritual truth. It makes sense to them. They may not always accept it or obey it, but they get it. They have a choice to listen to it and allow the Holy Spirit to use it to transform their lives, or they can simply choose to act as if they never heard it. But they know what they heard. They know what the Spirit has said. So even in our disobedience we know that He is there. And that too, should give us assurance. Conviction should be comforting. It should remind us that God is there, in the form of His Spirit. By this we know that we are His children, because He has placed His Spirit within us, to comfort, convict, guide, empower, help and teach us.