In the past few years I've grown increasingly concerned about the confusion that seems to exist in the minds and hearts of many over the difference between principle and practice. Principles are bedrock, unchangeable anchor points, rooted in Scripture and theologically framed, that provide the paths we need to walk in wisdom. Practice is the application of such principles in various spheres of life, and these, unlike principle, vary from place to place, culture to culture, and time to time.When someone confuses practice and principle they become sectarian legalists, demanding all practices conform to their practices, wrongly imagining that they are pointing people to the unchangeable. In doing so they are sending the message, "If you were a REAL Christian - like me - you'd do it my way."
Let me note some brief examples.
Worship: The principle that we are to worship God in Spirit and Truth is unchangeable; the practice of that worship varies across cultures and churches and times and will continue to do so. When someone confuses practice and principle they become sectarian legalists, demanding all practices conform to their practices. When someone says 'this liturgy' and no other, 'this music' and no other, or 'this amount of time' and no other, they've entered into a realm of sectarianism. That doesn't make all practices valid of course - people and churches can and do invent and practice things in worship that are contrary to principle. But the principles of worship, articulated by and rooted in Scripture, have to be applied in various settings. The arrangement of the furniture, the volume of the sound, the style of the music, the garb of the leaders, and the length of the service are not principle issues but practice issues. Even something one believes is principled - Lord's Day Eucharist using real wine and bread - has to be viewed in terms of recovery and reform, not revolution and demand. We have to teach principles and then learn to apply them in wise practices. That takes time.
Education: The principle is that parents are responsible for the education of their children. HOW they see to that is a matter of practice and it will vary over time (in the child's life) and from place to place. I am deeply alarmed when I hear a parent insist that there is only one possible PRACTICE of education - their way of course - and that those Christians who don't do it their way are deficient in their faith, or worse. Educating at home is one possible practice of the principle of Education. So are Christian day schools. So are co-ops. So are non-Christian state sponsored schools funded by tax dollars. NO practice is free from sin and its consequences and all have their dangers. Its odd to me that some homeschool families, having felt derided and rejected in some church, leave for a more 'home-ed friendly' church and then turn right around and treat contemptibly any family that doesn't educate at home. I've even seen this done among home schoolers over the different approaches to home schooling! The same is true in terms of education philosophy; massive debate takes place over which approach to education is more 'Christian' than another, sometimes leaving faithful Christians in places of aggravated dispute over this as though the subject were as vital as some part of the Nicene Creed.
Courtship and Marriage: The principle that a man shall leave his parents and cleave to his wife is clear; the practice of how that arrangement is made is a matter of practice. There are a host of ways that parents these days assist their children in discovering a person to marry. Some children grow and move away from home, marrying much later and without as much reference to the parents back home. Insisting that one particular approach is more Biblical than another on this matter is folly. One cannot simply lay the world of the Bible (worlds!) across our landscape and expect it to fit without some bumps and air pockets. Typically gals don't marry in their early teens now (how many sermons have you heard mentioning Mary's age at the time of Gabriel's visitation?), and typically people then did not travel as far or as frequently as we do, or pursue the same educational qualifications for professional life. Don't fall into the trap of thinking that there is only one way that God can arrange a marriage - he's the One, after all, who is the author of married life.
I could mention others, but I'll leave it there for now. You get the idea. There are matters of 'first importance' (1 Corinthians 15:1ff), matters of principle that cannot and must not be overthrown and which are the basis of the Christian community. Secondary issues are just that and if one makes them primary, one is lighting the fuse for sectarian division rooted in arrogant presumption. Humble love brothers and sisters, humble love is the way to approach all the secondary issues. The old proverb remains true: "In essentials, unity; in non-essentials, liberty; in all things, charity."