Clothed with righteousness
I will also clothe her priests with salvation...
Compare this with verse 9: “Let Your priests be clothed with righteousness...”
To be saved is to be righteous. This has several layers of meaning.
First, to be saved is to be declared righteous, to have entered the saving protection of Jesus Christ Who has paid the price for and taken away all our unrighteousness. We are thus justified to come before God and call Him Abba, Father.
Second, I think we might say there is an inward reorienting of the soul, so that becoming righteous is established as a defining priority (Matt. 6.33), understanding what this entails shapes all our thoughts (2 Cor. 10.3-5), and desiring righteousness - which is to say, desiring the Lord Himself - is our greatest joy and highest delight (Ps. 37.4). We must be always about this work of orienting our soul for righteousness, for we too easily drift from this, the path of salvation.
Third, we expect to increase in righteousness, albeit not a righteousness of our own. Rather as Jesus is formed in us (2 Cor, 3.12-18), we evidence His work within us by the obedience of righteousness in our daily lives.
Finally, we look forward to that day when sin will be no more and we will be wholly like Jesus, in perfect righteousness, because we will see Him as He is 1 Jn. 3.1-3). Thus desiring righteousness and becoming righteous are defining attributes of one who is truly saved.
Peter reminds us that we are a "royal priesthood" in our Lord Jesus Christ. And He intends that we should be clothed with His righteousness, that we should put on the Lord Jesus Christ and make no provision for the lusts of the flesh, that we should learn Jesus, grow in Him, and be increasingly conformed to His likeness. They who are truly saved will work out their salvation in fear and trembling so that they bring holiness (righteousness) to completion in the fear of God.
They who are indifferent to increasing in righteousness should consider whether they are truly saved, or are yet lost in their sins and deceiving themselves (2 Cor. 13.5). And they who are entrusted with the ministry of the Word must realize that the goal of all their preaching and teaching must be to present all those who are entrusted to their care complete in Jesus Christ and in the fullness of His righteousness.
To be saved is to be righteous, and increasing in it. To make disciples is to encourage and assist those who are saved in realizing this high and holy calling, even as they also press on for the same.