O God, thou art terrible out of thy holy places - The places where thou dwellest, and from which thou dost manifest thyself. That is, The manifestations which thou dost make of thyself when thou seemest to come forth from thine abode are "terrible," or are suited to fill the mind with awe. Compare Psalm 45:4, note; Psalm 65:5, note; Psalm 66:5, note.
The God of Israel - The God who is adored by Israel, or by his true people; our God.
Is he that giveth strength and power unto his people - He is not weak and feeble. He is able to protect them. He shows that he can gird them with strength; that he can defend them; that he can sustain them in the trials of life. The God whom they acknowledge as their God is not one whose strength fails, or who is seen to be feeble and powerless when his aid is needed. He is fully equal to all their needs, and they never trust him in vain. "Blessed be God." For all that he is, for all that he has done. This is the language of joy and praise in view of the contemplation of his character as depicted in the psalm. At the close of every right contemplation of his character, his government, his plans, his claims, his law, his gospel, the heart that is right will say, "Blessed be such a God." To one endowed with "such" attributes, praise - everlasting praise - is due.

O God, thou art terrible out of thy holy places - The sanctuary and heaven. Out of the former he had often shone forth with consuming splendor; see the case of Korah and his company: out of the latter he had often appeared in terrible majesty in storms, thunder, lightning, etc.
He that giveth strength and power unto his people - Therefore that people must be invincible who have this strong and irresistible God for their support.
Blessed be God - He alone is worthy to be worshipped. Without him nothing is wise, nothing holy, nothing strong; and from him, as the inexhaustible Fountain, all good must be derived. His mercy over his creatures is equal to his majesty in the universe, and as he has all good in his possession, so is he willing to deal it out, to supply the utmost necessities of his creatures. Blessed be God! The Arabic adds, Alleluiah!
The best analysis I find of this Psalm is that by Bishop Nicholson. I shall give it at large, begging the reader to refer particularly to those passages on which the preceding notes are written, as in some of them the analysis gives a different view of the subject. The old Psalter gives the whole Psalm a spiritual and mystical interpretation. And this is commonly the ease in the commentaries of the fathers.

O God, [thou art] (d) terrible out of thy holy (e) places: the God of Israel [is] he that giveth strength and power unto [his] people. Blessed [be] God.
(d) In showing fearful judgments against your enemies for the salvation of your people.
(e) He alludes to the tabernacle which was divided in three parts.

O God, thou art terrible,.... In his judgments and acts of vengeance, on antichrist and the antichristian states; being the Lion of the tribe of Judah, that will break them to pieces as a potter's vessel: or "reverend" (s); to be feared and worshipped by his saints;
out of thy holy places; both out of heaven, the habitation of his holiness, by angels and glorified saints there; and out of all his churches, the several assemblies of them, among whom he is greatly to be feared and adored: the Targum interprets it of the house of the sanctuary;
the God of Israel is he that giveth strength and power unto his people; his peculiar covenant people, his Israel he is the God of. These are weak, and encompassed about with infirmities; he has strength in himself for them; he has promised it to them, and he gives it to them as a pure gift and unmerited favour of his. It may be understood of the great degree of strength that will be given them in the latter day; when a small one shall be a strong nation, and the feeble shall be as David, and David as God, as the Angel of the Lord, Isaiah 60:21; and of the dominion and greatness of the kingdom under the whole heaven; which will be given to the saints of the most High, Daniel 7:27;
blessed be God: the psalm is concluded with an ascription of blessing to the Messiah, who is God blessed for evermore; and who, as Mediator, is the promised seed, in whom all nations were to be blessed, and now will be; see Revelation 5:12.
(s) "venerandus", Michaelis.

Terrible - Deservedly to be feared.