86. Since then we are redeemed from our misery by grace through Christ, without any merit of ours, why should we do good works?
Because Christ, having redeemed us by His blood, also renews us by His Holy Spirit after His own image, that with our whole life we show ourselves thankful to God for His blessing, and also that He be glorified through us; then also, that we ourselves may be assured of our faith by the fruits thereof; and by our godly walk win also others to Christ.
Heidelberg Catechism (1563) 86 (Here is a longer explanation of Heidelberg 86.)
Kevin Deyoung—“There are duties man owes to God and blessings that are connected to the exercise of these duties, even if–and this is important–God is the one who sees to it that these duties are carried out. Heaven cannot be reached without good works (Heb. 12:14; Rev. 21:27…. Turretin observes, “ Good works are required not for living according to the law, but because we live by the gospel….”
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Deyoung—“If, on the one hand, we say no, good works are not necessary, we can hardly make sense of the warnings and moral imperatives of the New Testament. But if we say good works are necessary to salvation, it can sound like we’ve suddenly made heaven the product of our effort and obedience. But that’s not what Hebrews 12:14 means, nor what Turretin means. Read carefully this paragraph: Works can be considered in three ways: either with reference to justification or sanctification or glorification. They are related to justification not antecedently, efficiently and meritoriously, but consequently and declaratively. They are related to sanctification constitutively because they constitute and promote it. They are related to glorification antecedently and ordinatively because they are related to it as the means to the end. (XVII.iii.14)
Deyoung–“Good works are identified with sanctification as its definition and cheerleader.”
http://www.thegospelcoalition.org/blogs/kevindeyoung/2015/10/08/are-good-works-necessary-to-salvation