The darkness of depression is so scary because it seems hopeless. You think you will not find hope again, you desire fellowship but are trapped in a place where you cannot bear to experience it, the lonliness and isolation it carries feels so desperate. You may even feel like God has abandoned you. It is a vulnerable place.
It is a place where you need to know truth because the easiest thing seems to be to just get out. Many are tempted with thoughts of suicide. Others may be tempted to run to mind numbing substances or activities. It is the most horrific feeling that lingers. Unlike most physical pain which can be hard but managed the depressive person is trapped, at the mercy of the darkness until it lifts. You cannot run away, you cannot escape it. You cannot read enough Scripture or play enough praise songs. It can persist for a long time. So what is the point?
Though we cannot understand fully (because there are many things that can cause depression and it can vary in many degrees), it is something that God has allowed, we must remember that He is sovereign over all things. The enemy of our souls cannot bother us any more than God permits. If we are thinking lies or believing lies these do come from the enemy because Scripture calls him the father of lies.
Keep reminding yourself of the truth you know, the promises that are ours in the Scriptures. Christ can relate to this, He felt it. His soul was anguished to the point of death in the garden while He was praying and pondering the cup He had to bear. Yet He chose obedience. No one will ever experience the pain and emotional turmoil that Christ endured. He understands and is with you through this. We must believe He is and persevere in faith.
If we want to take our life it is a ploy or temptation from the enemy because he comes to steal, kill, and destroy. Don't fall for his traps in this time. He will hit you and not play fair though you are in a dark pit with no protection it seems. Remember the truth that God loves you. He is the only rightful person that can give and take life. He has written all your days out in His book. He will fulfill His promises. Remember all He has done.
Depression is not fun. It is a hard type of suffering to endure. I get so exhausted when I am struggling with it. You must keep your mind disciplined to take any wrong thoughts captive and make them obedient to Christ. It is exhausting but necessary. Do not hide it from others, request help of friends who will send you Scripture to encourage you. Enlist friends to pray for you. Talk to someone who you consider safe about what is going on in your head. This will help you not be alone and help you stand accountable with someone. Don't feel bad if you need medication to help you. We live in a broken world and our bodies are broken as well. Sometimes we need additional help through medicine. It is nothing of which to be ashamed.
One thing that depression does for me is enhance my longing for Heaven. It reminds me that this is not my home. I was made for a perfect place that one day will become a reality. I do not get to chose when that day is, my body was bought at a high price by Christ on the cross shedding His blood and tears for me. So as I live I am to live for Christ. He has plans and purposes for us with each breathe He gifts. Fix your eyes on HIM, remember it will not last forever. Hang tight to His promises and believe this temporary trial will show your faith of greater worth than gold as you endure and trust and in turn will bring Him much glory.
If you are walking alongside someone who is depressed, be patient. It is a hard road to walk and walking it alone is even more difficult. Walk with them, patiently love them, endure it with them. DO NOT tell them to get over it or determine the end time of their suffering. If a depressed person could just get over it they would. No one would chose this kind of suffering. Love them and encourage them in the gospel. Remind them of His promises. Remind them of His great love. Point them to the cross. Pray like crazy. Don't give up on them. Endure like a good soldier. Your support is cherished though a depressed person may not be able to express that at the moment. Love without expecting anything back. Be an example of Christ to them.