Revelation 4:8

And the four beasts had each of them six wings about [him],
&c.] As the seraphim in ( Isaiah 6:2 ) with two of which they might cover their faces as they did, testifying thereby their reverence of God, when in his presence; and with the other two cover their feet, signifying their sense of their sinfulness, weakness, and imperfection, in their conversation, even in their best works, and in the ministry of the word; and with the other two fly about, as denoting their readiness to minister the word and ordinances, to visit the members of the church, and do all good offices of love and service to them that lie in their power:

[and they were] full of eyes within;
to look into the sin and corruption of their own hearts, which is a means of keeping them humble amidst all their attainments, gifts, and graces, and of qualifying them to speak aptly of the cases of others; and they have eyes within, to look into and consult their own experience; for besides the word of God, which lies before them, they have a testimony in themselves of the truth of the doctrines of the Gospel, which they do well to attend unto; and they have these inward eyes to look into that treasure which God has put into their earthen vessels, in order to bring out of it things new and old.

And they rest not day and night;
they give up themselves to the ministry of the word, and prayer; are wholly in these things, meditate on the word continually, and preach the Gospel in season, and out of season:

saying, Holy, holy, holy, Lord God Almighty, which was, and is, and
is to come;
living under a continual sense of the holiness of God, Father, Son, and Spirit; and how necessary holiness is in themselves, who bear the vessels of the Lord, and in the churches and house of God; taking care that all their doctrines are according to godliness, and serve to promote holiness of life and conversation; and also under a sense of the power of God, and of their need of it, to carry them through their work, and make their ministry successful; and of the eternity and immutability of God, which is a wonderful support unto them amidst all the difficulties and troubles that attend them. The word "holy" is three times used here, as by the seraphim in ( Isaiah 6:3 ) ; and in some copies it is repeated six times, and in others nine times, as in the Complutensian edition.