And be not grieved and depressed, for the joy of the Lord is your strength and stronghold. Nehemiah 8:10
The definition of a stronghold is a place of security or a fortified place. This scripture is telling us that the joy of the Lord is not only our strength, but it is protective. Being joyful or grateful, has healing effects on the mind, body and spirit. When we are joyful or happy, our heart releases atrial natriuretic hormone that lowers blood pressure and reduces anxiety. The joy is the Lord is experienced when we truly understand the benefits of being in Christ. Scripture tells us that as believers, we are in Christ and seated in heavenly places. Psalms 28:7 states that the Lord is our strength and impenetrable shield. Being in Christ means that we are surrounded or encased in His love and protection. It is like wonder woman in her invisible plane, she is protected even if she cannot see the plane around her.
You love him passionately although you have not seen him, but through believing in him you are saturated with an ecstatic joy, indescribably sublime and immersed in glory. 1 Peter 1:8