“This is how we know that He lives in us; we know it by the Spirit He gave us.” 1 John 3:24 “The Spirit himself testifies with our spirit that we are God's children. Now if we are children, then we are heirs—heirs of God and co-heirs with Christ, if indeed we share in his sufferings in order that we may also share in his glory.” Romans 8:16-17 God’s Spirit talks to our spirit to tell us that we belong to Him. We are His children. I cannot explain it. But to those to whom this has happened it does not need explaining.
Jeremiah 17:7-8: "Blessed is the man that trusteth in the LORD, and whose hope the LORD is. For he shall be as a tree planted by the waters, and that spreadeth out her ROOTS BY THE RIVER, and shall not see when heat cometh, but her leaf shall be green; and shall not be careful in the year of drought, neither shall cease from yielding fruit."