Actually, my definition of legalism is not strictly mine, nor an original invention. Further, this rather common defition of legalism is derived directly from what Jesus said. "And He said to them, "Rightly did Isaiah prophesy of you hypocrites, as it is written: 'THIS PEOPLE HONORS ME WITH THEIR LIPS, BUT THEIR HEART IS FAR AWAY FROM ME. 'BUT IN VAIN DO THEY WORSHIP ME, TEACHING AS DOCTRINES THE PRECEPTS OF MEN.' "Neglecting the commandment of God, you hold to the tradition of men." He was also saying to them, "You are experts at setting aside the commandment of God in order to keep your tradition." (Mark 7:6-9)
So, legalism is being an expert at inventing laws that God never delivered to men. Worse, legalism is imposing those invented laws on others.
Just realized something, but prior explication is needed.
First, take careful notice of what these extra commands are for: setting aside God's commands (as any orthodox or traditioanl Jew Jew will tell you the Rabbis rightfully do to this day). If we get at the very essence of legalism, it's not making commands, which is merely one form legalism takes to happen, a symptom, or secondary thing... (need to think that part out a bit), but the overriding, setting-aside, or 'trying to wiggle out' of commands: it's 'lawyering' in the sense lawyers take words and seek 'legalistic' loopholes, 'strict to the letter', circumventing, or rebelling against, the sense, the spirit; this is the proper use of the term 'legalism', and as stated above, command-adding is one way to do it, that is, in-place-of God's commands. In the strict sense, if an added commanded theoretically didn't set-aside any of God's commands (though I don't believe that's possible since one in the word is not to accept additions, or the adders), it wouldn't be legalism--though still wrong.
It's worth noting the term is thrown-around for the mere suggestion of 'do's and don'ts', but as one apologist put it, '[suck it up], there are 'do's and don'ts'. Rules are legalism, rules to avoid or justify circumvention or disobedience to the rules/commands is, (obedience to rules in hopes of being saved, on the other hand, is attempting to make one's own works-righteousness before God: also one aspect of some forms of legalism--but just becuase this is so, doesn't mean there aren't rules, or that the rules, the commands, shouldn't be obeyed, emphasized, asserted, etc.).
With that explanation, there's one more piece needed: 'tradition'. We use the word as 'something passed down over time', or 'done because it's done before', but it's simpler in Scripture, so far as I know, (even Paul commends the Corinthian Church for keeping 'my tradition', that he delivered to them 'from the Lord'): it's something 'passed on', 'given'.
This is where it gets interesting: I've mentioned here the (very official, present, pastor-taught) teaching that "if one must obey God or men who are you're leaders, you're to obey your leaders, and in so doing you're trusting God by trusting your leaders, so that if they've erred it's they who'll be held accountable"; this was not denied by those I confronted over it--indeed they INTENSELY fought in favor of it, asserting it, 'NO, I MUST TRUST MY LEADERS': this is what GC teaches its leaders in the leader meanings, training, etc., this was a young man (not even a year older than I am) who, really sadly, has more than a few biblical issues: some of such essential importance that I won't even give him company anymore (insisted that Jesus's human nature, rather than being a Second Adam's, was enticeable--tempteable from within, rather than untemptable (God cannot be tempted), and I even explained to him the several greek uses/senses of the word, and how it is applied in the contexts where Jesus was 'tempted' and where it says both that God cannot be 'tempted' yet Jesus can emphatize with us for knowing our sufferings--in his mind 'suffering' genuinely meant Jesus suffered from not fulfilling sinful desire, or that sort of thing; there's one error of overemphasizing His Deity, eclipsing His humanity, the reverse of that, but also, defining 'Humanity' as 'having a fallen nature' (as the term is used by us of other people: Scripture presents Jesus as having continuity--and discontinuity--with us; as God He's not like us; as man, He's like us, yet but unlike us, as God, and as the Second and last Adam, in Him was, is, no darkness or variableness of turning: that was the termination of any genuine relationship between us, for he asserted, and clings to, another Christ: a Christ who could desire sin (rather than good things, but which Satan and the world 'tried' His nature/natures by presenting them in such a way that partaking would be sin: sin is, after all, the misuse of all that good which God has made us, the fulfillment of desires through wrong means).
For a moment, in regards the GC* teaching on obeying leaders, we'll push aside the promise of Scripture that each is punished for their own sin and responsible (both obeyer of leader over God and that leader are culpable in this case).
In this case, too, which they know, it's teaching of obeying men over God, which Scripture is explicitly clear, which Jesus is clear, is not to be done; notice, though...this is the essence of legalism. GC* in that sense is every bit like the Pharisees, and explicitly condemned by Scripture, the very kind of false prophets and wolves it warns the sheep to beware, and for Christians to expose publicly and reject: it's not Christian for that: just this connection here demands I say so. All the more reason to oppose the wicked misleaders.
BEWARE THE LEAVEN OF THE PHARISEES. --Jesus Christ, God incarnate, Son of God, the only begotten, ONLY Head of the Church, Authority over all.
And with that at least five people or so will know who I am, not that if they're reading they wouldn't recognize anyways. : )