Apparently the writers of the Heidelburg Catechism never thought of simply finding the phrase "good works" in Scripture, and then making up their minds. Here are a few:

Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven. Matt 5:16

Jesus answered them, Many good works have I shewed you from my Father; for which of those works do ye stone me? Jn 10:32

Now there was at Joppa a certain disciple named Tabitha, which by interpretation is called Dorcas: this woman was full of good works and almsdeeds which she did. Acts 9:36

For rulers are not a terror to good works, but to the evil. Wilt thou then not be afraid of the power? do that which is good, and thou shalt have praise of the same: Rom 13:3

For we are his workmanship, created in Christ Jesus unto good works, which God hath before ordained that we should walk in them. Eph 2:10

But (which becometh women professing godliness) with good works. I Tim 2:10

Well reported of for good works; if she have brought up children, if she have lodged strangers, if she have washed the saints' feet, if she have relieved the afflicted, if she have diligently followed every good work. I Tim 5:10

Likewise also the good works [of some] are manifest beforehand; and they that are otherwise cannot be hid. I Tim 5:25

That they do good, that they be rich in good works, ready to distribute, willing to communicate; I Tim 6:18

That the man of God may be perfect, throughly furnished unto all good works. II Tim 3:17

They profess that they know God; but in works they deny [him], being abominable, and disobedient, and unto every good work reprobate. Titus 1:16

In all things shewing thyself a pattern of good works: in doctrine [shewing] uncorruptness, gravity, sincerity, Titus 2:7

Who gave himself for us, that he might redeem us from all iniquity, and purify unto himself a peculiar people, zealous of good works. Titus 2:14

[This is] a faithful saying, and these things I will that thou affirm constantly, that they which have believed in God might be careful to maintain good works. These things are good and profitable unto men. Titus 3:8

And let ours also learn to maintain good works for necessary uses, that they be not unfruitful. Titus 3:14

And let us consider one another to provoke unto love and to good works: Heb 10:24

Having your conversation honest among the Gentiles: that, whereas they speak against you as evildoers, they may by [your] good works, which they shall behold, glorify God in the day of visitation. I Pet 2:12

It astounds that *none* of these verses are used in the list given under your catechism. I'm sure the ones mentioned have some bearing on the concept. Just as I'm sure the writers were more concerned with opposing Romish ideas and upholding Reformer dogma than they were with simply letting Scripture speak for itself.

All of these verses that mention good works seem to me very far from the idea of following the Mosaic law. The idea of perfection, or purity, becomes fruitfulness, not sterility.

If I were to picture a Calvinist's mind, it would be pristine and spotless, like some kind of stainless steel machine. But I think a more healthy mind might depict purity as a tree planted by streams of water, bearing fruit in season, its leaf never withering.

Good works should be alive, and should take cultivation, and effort on our part. They don't just happen because we're justified. They take work.

What's at stake in the difference between works of the law and good works is this very idea of a tree. It can grow, or it can wither and die. Someone's faith can grow; it can wither. It can die. When Christ heals one of the blind men, he sees men as trees walking.