Before I started studying it, I knew not much about doctrines. I knew God’s message, a few things here and there, but had someone asked me about doctrines, I would have answered “no idea; ask someone else!”. So I am perfectly fit to tell you: the study of doctrines is important, to understand and apply better God’s Word, for different reasons.
The first is that it does enhance your understanding of the Word. Let me put it this way: the study of doctrines shows you the whole picture, the deeper meaning behind verses put together in a different way, for them to be seen under a different light. For example, if you study and regroup the following verses together, you can find the term “gospel” used six times, for six different meanings: Romans 1:16-17 (gospel of Christ), Romans 2:16 (my gospel), 2 Corinthians 4:3-4 (our gospel), Ephesians 6:15 (gospel of peace), Revelation 14:6 (the everlasting gospel) and Matthew 24:14 (gospel of the Kingdom). Two other examples would be: the conditions for fruits of the spirit and the five possible cycles of discipline. Conditions of the fruits of the spirit (Gal 5:22-23) are given throughout the bible: contact with Living Water (Psalm 1:3, Ezekiel 47:12), spiritual receptivity (Matt 13:23), death of the old life (John 12:24) and abiding in Christ (John 15:4). It also mentions the risk of chastening (John 15:2). The five cycles of discipline are found, however, in one entire passage: Leviticus 26:14-29. To conclude, I would say that studying a specific doctrine sorts out all the precious, yet random information given to us about it in the Word. A good example would be the fundamentals of believing given straight in 1 Corinthians 15:1-4 or Satan’s personality resumed in two paragraphs: Ezekiel 28:11-19 and Isaiah 14:12-17.
The second is that it can help you improve your teaching and/or witnessing. From my experience, studying doctrines seems to give the vocabulary to explain important ideas gleaned from God’s Word. It seems to be transcribing the Word’s message into our language, and verses back up. For example, to teach the Holy Spirit in depths but also in a structured way, you can teach the difference between “indwelling” and “filling”, the importance of our “relationship with Christ”, what it means and entails. Knowing about the fruits of the Spirit is great, but the study of the relevant doctrine will give you vocabulary to talk about what they are (ie difference between impersonal love and personal love, what is “faith-rest) and how to “bear fruit”. Also, the importance and meaning of prayer: looking up verses will tell you important people’s prayers (where, when and what…) and what answers came (prayer answered or not, how…). Studying the related doctrine can tell you the four types of answer you usually get from prayer, why and how those people prayed: prayer and studying the Word is our way to communicate with God, we have none other. In prayer, you should include confession of sin, adoration and thanksgiving, praying for others, then praying for yourself. Of course, you find all this information in the verses, yet through studying the doctrine you have the “jargon” and the ideas sorted out in a more structured way. This is essential, I believe, for teaching and witnessing. Studying the doctrine of anger, for example, shows you how it can easily be a sin, but not always: you can then explain the difference between “divine anger” and “sinful anger”. I would say verses mention the themes and doctrines explain them to me.
Studying doctrines has many benefits: we learn about our identity in Christ (citizenship, inheritance), our responsibilities (growth, relationship with Christ, witnessing), the meanings and usefulness of suffering along with how this world works and Satan’s past (five “I will”s, three falls) and strategies (with believers and non-believers)… The advice I’d give is to combine your learning of doctrines with the verses; as you usually memorize something because you’ve understood it, what it tells you and where it comes from. An easy example in mind is Ephesians 6:10-18, how the Bible is our best weapon against the Devil’s strategies: our faith is our shield, the Word our sword. God’s power our helmet, his justice our armor. What do these words (“jutice”, “power”, “faith”, etc) from the verses entail? Another advice would be: doctrines give you more “human language” or witnessing and teaching, but you have to simplify it (ie words such as “indwelling” or “justice of God”, “omnipotent”, “omniscient”, etc) to make yourself understood from others, especially novice Christians or non believers.