The expectation of the godly: "The sun of righteousness shall rise"

"It was not in vain that God of old willed, through expiations and sacrifices,
to attest that he was Father, and to set apart for himself a chosen people. Hence, he was then surely known in the same image in which he with full splendor now appears to us. Accordingly, after Malachi has bidden the Jews heed the law of Moses, and continue in it earnestly because after his death there was to be an interruption of the prophetic office, he immediately afterward declares: “The sun of righteousness shall rise” [Malachi 4:2].

By these words he teaches that while the law serves to hold the godly in expectation of Christ’s coming, at his advent they should hope for far more light. For this reason, Peter says: “The prophets …searched and diligently inquired about this salvation,” which has now been made manifest by the gospel [1 Peter 1:10]. And “it was revealed to them that they were serving not themselves,” or their age, “but us, in the things which have …been announced” through the gospel [1 Peter 1:12].

Not that the teaching of these things was useless to the ancient people or without value for the prophets themselves, but because they did not come to possess that treasure which God has transmitted to us by their hand! For today the grace of which they bore witness is put before our very eyes. They had but a slight taste of it; we can more richly enjoy it. Accordingly, Christ declares that Moses bore witness to him [John 5:46], yet He extols the measure of grace in which we surpass the Jews. For he addresses his disciples: “Blessed are the eyes which see what you see; and blessed are the ears which hear what you hear. For many kings and prophets longed for this and did not attain it” [Luke 10:23-24; Matthew 13:16-17]. That God has preferred us to the holy patriarchs, who were men of rare piety, is no slight commendation of the gospel revelation." -- John Calvin, Institutes of the Christian Religion, v. 2, ch. 9

While God through his divinely given wisdom protects his saints from those who are covenant-breakers, God through his divinely given wisdom protects his saints for eternal life. Because "wisdom will come into your heart" (Proverbs 2:10), "you will walk in the way of the good and keep to the paths of the righteous" (Proverbs 2:20).

There are parallelisms Solomon is using to show that God's initial action of guarding and protecting his saints via wisdom will result in Solomon's son living wisely. Solomon does this in his use of the words "way" and "path". So, the parallelisms look like this:

The Lord is a shield watching over the way of his saints (vs. 8).
“His saints” will walk in the way of the good (vs. 20).

IOW, God watches or protects. We walk.

And again,

The Lord is a shield guarding the paths of justice (vs. 8)
“His saints” will keep to the paths of the righteous (vs. 20).

IOW, The Lord guards. We keep or protect (the same word used for keep in Genesis 2:15).

Our walk in wisdom isn’t something we do on our own. God's action results in our response. Wisdom cannot be manufactured within us. It must given to us from someone outside of us. We walk and we protect and guard because God is shielding us first. The endpoint or the goal of God’s shielding for his isn’t merely the paths of justice or the paths of the righteous but the destiny of those paths: eternal life itself. Verse 19 says the wicked will never regain the paths of life. The implication is also true: there are those who are on the very same paths of life who will not stray from it. This implication is made more explicit in verse 21 which says the upright or those who fear the Lord "will inhabit the land". There is a future consideration of God's guarding and protecting his people through wisdom. Because God "shields", "guards" and "protects", keeping the wise on the path of life, ultimately “His saints” will inhabit the land.

The new covenant implications of what Solomon is saying here should be fairly obvious to those of us in the new covenant: it is impossible to act wisely or make right decisions without having first been given wisdom breathed by God into the heart (Proverbs 2:6 and 2:10). It is impossible to understand righteousness, justice, and “every good path” without having been given wisdom from God’s mouth into our heart. This is the new heart of the new covenant (see Ezekiel 36:26 and Ezekiel 37:5). As God breathes wisdom into the new heart (vs. 10), Wisdom is incarnated in the recipient through discretion and understanding that guard or watch or put a hedge around the path of life (vs. 11), so that the recipient through wisdom ultimately arrives at the inhabitation of the land in Christ himself.