The psalmist returns thanks to God for giving him the victory over his enemies; which victory he had earnestly requested, Psalm 21:1, Psalm 21:2. He enters into a detail of the blessings that in consequent of the victory he had obtained, Psalm 21:3-7. He predicts the destruction of all those who may hereafter rise up against him, Psalm 21:8-12; and concludes with praising the power of Jehovah, Psalm 21:13.Adam Clark Commentary
Psalm 21 English Standard Version (ESV)
The King Rejoices in the Lord’s Strength
To the choirmaster. A Psalm of David.
O Lord, in your strength the king rejoices,
and in your salvation how greatly he exults!
2 You have given him his heart’s desire
and have not withheld the request of his lips. Selah
3 For you meet him with rich blessings;
you set a crown of fine gold upon his head.
4 He asked life of you; you gave it to him,
length of days forever and ever.
5 His glory is great through your salvation;
splendor and majesty you bestow on him.
6 For you make him most blessed forever;[a]
you make him glad with the joy of your presence.
7 For the king trusts in the Lord,
and through the steadfast love of the Most High he shall not be moved.
8 Your hand will find out all your enemies;
your right hand will find out those who hate you.
9 You will make them as a blazing oven
when you appear.
The Lord will swallow them up in his wrath,
and fire will consume them.
10 You will destroy their descendants from the earth,
and their offspring from among the children of man.
11 Though they plan evil against you,
though they devise mischief, they will not succeed.
12 For you will put them to flight;
you will aim at their faces with your bows.
13 Be exalted, O Lord, in your strength!
We will sing and praise your power.
Poetry by Isaac Watts based Psalm 21
Our king is the care of Heaven.
The king, O Lord, with songs of praise,
Shall in thy strength rejoice;
And, blest with thy salvation, raise
To heav’n his cheerful voice.
Thy sure defence through nations round
Has spread his glorious name;
And his successful actions crowned
With majesty and fame.
Then let the king on God alone
For timely aid rely;
His mercy shall support the throne,
And all our wants supply.
But, righteous Lord, his stubborn foes
Shall feel thy dreadful hand;
Thy vengeful arm shall find out those
That hate his mild command.
When thou against them dost engage,
Thy just but dreadful doom
Shall, like a fiery oven’s rage,
Their hopes and them consume.
Thus, Lord, thy wondrous power declare,
And thus exalt thy fame;
Whilst we glad songs of praise prepare
For thine almighty name.
The Bible tells us that the son of David will soon emerge from the heavenly temple amidst the blowing of trumpets to receive His rightful kingdom and to destroy the wicked. Read more about this prophecy here