‘YHWH is King for ever and ever,
The nations are perished out of his land.
YHWH, you have heard the desire of the meek:
You will establish their heart,
You will cause your ear to hear,
To judge on behalf of the fatherless and the oppressed,
That man who is of the earth,
May strike terror no more.
The psalm, which began with such hopelessness, finishes with the triumphant picture of the everlasting kingdom, with YHWH established as everlasting king, all adversaries and unrighteous thrust out and dealt with, and the meek and the fatherless and the oppressed living quiet lives in full confidence of true justice, and treated with respect by all. In Isaiah's words, the lions will lay down with the lambs, for no one will any longer strike terror into anyone else. It will not be men of the earth who control things, but God. Righteousness will reign supreme. The picture is of total divine dominance by God, dwelling in His light.
‘YHWH is King for ever and ever.' His enthronement will be revealed and His rule over His own will from then on be permanent for ever.
‘The nations are perished out of his land.' The land that He promised His people will now be free of all enemies, of all who defile it and of all unrighteous men. The first thought is probably of the final fulfilling of God's requirement that ‘the nations' who had dwelt in Canaan should be thrust out as God had previously commanded, so that all pernicious influences would be removed. But it can also include any nations who had trespassed on God's land and introduced pernicious influences. And with them would be thrust out all who followed in their ways and thus identified with them.
So those who are without, and even more importantly, the quislings within, will be removed from the land, which will thus be purified. The thought is clearly that the unrighteous were seen as unrighteous because they did not respond to YHWH but submitted to subversive influence, the ways of the godless nations. Thus all these will now have been destroyed out of the land (compare Deuteronomy 8:19-20). It will be the land of His inheritance as it was intended to be, a land of eternal bliss, where all worship YHWH and are obedient to His will. Ancient Israel had no conception of a possible heavenly kingdom and thought in terms of permanent and fruitful possession for ever of the land that God had given them and a possession which was under God's personal rule, where all responded to Him.
And this will be because YHWH has heard the cries of the meek and lowly. Though they had cried to Him day and night for what had seemed so long, now He would avenge them speedily (Luke 18:8). In the end His will will be done. All fear will be done away. The future will be eternally secure in righteousness.
Jesus and the Apostles reinterpreted this in terms of the everlasting heavenly kingdom of which His own were citizens.