In chapter 10:38 the inspired writer has quoted habakkuk 2:4 and he is applying these words to the ongoing Christian life. We are saved; we have found Christ; now, what is the rule of life for the believer? It is faith, trust in God at all times.
Justifying faith focuses on Christ alone and obeying him in the gospel, but ongoing faith embraces other things also. It embraces the providence of God. Some terrible thing has happened to me, some unfortunate setback, some hurtful thing, some disadvantage, but faith asks, why has God permitted this? I must prove him in this experience, I must commit it to him. Perhaps he is chastising me for some neglect, some fault. If so, I will not have to search far, it will be pretty obvious to me what it is. Perhaps he is training me for my future Christian service: making me more sympathetic to others so that I can comfort others with the comfort I receive from God in this experience. Are you ready to look to him, never to think you are abandoned?
Do you reflect on spiritual things? Do you try to find time in your personal devotions not just to read, but to reflect also? As you reflect on spiritual things and as you pray for help, the things you read about in the doctrines you believe will become so real, so substantial to you. They will become deeply evident to you, and that is the basis of your Christian joy. Leave out what used to be called years ago meditation, leave out reflecting on these things, and you will not grasp them, they will not be real to you.