From Jason Hood
Psalm 98: God's public display of his saving righteousness calls forth exuberance and excitement from his creation (v 4-9), and praise from his people (v 1-3).
Far from being an aberration or blot on his character, God's judgment is an integral part of his salvation (v 9), and an accurate and vital dimension of who God is. After all, we're rejoicing before a King (v 6).
Psalm 99: Perhaps the most important dimension of God's status as King is that his presence brings with it holiness. As a result, those who stand in his presence must be holy, not least by exalting his name (declaring his greatness and his status as King), listening to his word, seeking his forgiveness, and obeying his commands (vs 3, 5, 7, 8). We also reckon with his holiness by acknowledging our need to come to him by virtue of mediators (v 6-7; and for us, through Jesus the Great Priest).
Psalm 100: Approaching a God this awesome requires the recognition of his holiness we see in Psalm 99; but it also requires and inspires gratitude and joy because (1) he made us, (2) his our faithful shepherd, and (3) God and his character are permanent in a world of temporary and transient things.
Romans 2.12-29: Paul shows in no small detail how his fellow Jews have broken the law (and on the basis of Romans 1, we can easily extrapolate, as Paul will in Romans 3, that *all* have sinned and fallen short of God's glory), and thus have no ground for boasting or assuming that they are "in" with God because they are circumcised and have received God's Word and affirmed it (or perhaps, because we have been baptized or give verbal assent to God's Word). Rather, Paul uses the Old Testament's "New Covenant" language to point to the possibility of being a Jew "inwardly," and having the heart circumcision from God that leads to obedience to God's commands, rather than relying merely on fleshly circumcision for approval from God.