When we repented at baptism we made a commitment to God to love Him with all our being and our neighbors as ourselves. Loving God means we obey all his commandments (John 14:15, 1 John 5:3). But just doing what God commands is not enough. To love God means to do His will in everything. This goes beyond the minimum of doing everything He says. This means we study the Bible diligently to know how God thinks and what He wants so we can please Him in everything.
This matter of doing God's will can separate those who are zealous for God from those whose love for God is lukewarm. Some people only want to do the minimum that is required. In studying the Bible, they do not go beyond learning if God commands something or not. Unless there is an explicit command about something, they consider themselves free to do whatever they want. But not everything God wants us to do is covered in a specific command. God teaches us principles, not just by commands and instructions, but by examples that show us God's thinking.
Herbert W. Armstrong taught this principle, and many doctrines he taught are based on it. You won't find explicit commands in the Bible about smoking, jury duty, makeup, birthdays, voting in national elections, etc. But Mr. Armstrong based his teaching of those subjects on the principle of going beyond the letter of the commands in the Bible to do what pleases God in everything.
Some people look at the specific do's and don'ts in the Bible to know what they can or cannot do, and then when a decision comes up that is not covered by any those explicit do's and don'ts, they base their decision on human reasoning only. A better approach is to study how God thinks so we can base every decision on God's will, whether that particular decision is explicitly explained in the Bible or not.
We are to do those things that are pleasing in God's sight (1 John 3:22). We should seek the Father's will, as Jesus did (John 5:30). Our food should be to do God's will (John 4:34). We should pray that God's will be done in our lives (Matthew 6:9-10), as Jesus did setting us an example (Luke 22:42). By learning from the Bible how God thinks and by seeking His will, we can apply God's Word to EVERY decision we make, not just those decisions concerning which God has given us a specific command. In this way, we can truly live by EVERY word of God (Matthew 4:4).
The Old Testament places great emphasis on obeying God's commands and laws. The New Testament also teaches obedience to God's commands, but places great emphasis on doing God's will.
"For this reason we also, since the day we heard it, do not cease to pray for you, and to ask that you may be filled with the knowledge of His will in all wisdom and spiritual understanding; that you may walk worthy of the Lord, fully pleasing Him, being fruitful in every good work and increasing in the knowledge of God" (Colossians 1:9-10).
"Now may the God of peace who brought up our Lord Jesus from the dead, that great Shepherd of the sheep, through the blood of the everlasting covenant, make you complete in every good work to do His will..." (Hebrews 13:20-21).
"But He answered them, saying, 'Who is My mother, or My brothers?' And He looked around in a circle at those who sat about Him, and said, 'Here are My mother and My brothers! For whoever does the will of God is My brother and My sister and mother' " (Mark 3:33-35).
"And do not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what is that good and acceptable and perfect will of God" (Romans 12:2).
"For you have need of endurance, so that after you have done the will of God, you may receive the promise" (Hebrews 10:36).
"And the world is passing away, and the lust of it; but he who does the will of God abides forever" (1 John 2:17).
See also John 9:31, Ephesians 6:5-6, and 1 Peter 4:1-2.
So when a doctrinal issue comes up for study or discussion, whether it be smoking, birthdays, jury duty, Church governance, or any other question that affects any decisions we make, the correct approach is to study that issue in the Bible asking not just what does God command, but what does the entire Word of God (including the examples that teach how God thinks) tell us about God's will on that issue.
Here are links to related sections in Preaching the Gospel:
Our Attitude and Approach Towards God's Word, Chapter 1
How to Understand the Bible, Chapter 1
The Days of Unleavened Bread - Repentance, Chapter 2
How to Obtain More of God's Help in Breaking Bad Habits, Chapter 7