And my tongue shall speak of thy righteousness - That is, I will praise thee as a righteous God.
And of thy praise - Of that which is a ground or reason for praise. I will speak continually of that in God and in his doings which make it proper that he should be praised.
All the day long - Continually; constantly. Every new proof of the kindness of God to him would lead to new acts of praise; and his life, as ours should be, would be a continual expression of thanksgiving.

And my tongue shall speak - I, who am chiefly concerned, and who have received most, am under the greatest obligation; and it will require the constant gratitude and obedience of my whole life to discharge the mighty debt I owe.

And my tongue shall speak of thy righteousness,.... In vindicating his cause, and bringing his enemies to shame and confusion, as well as of the glory and excellency of that righteousness of his, by which he was justified in his sight, and from whence his inward peace and prosperity flowed:
and of thy praise all the day long; for the many mercies, temporal and spiritual, he was every day favoured with.

In this praise of God's equitable government (Psalm 5:8) the writer promises ever to engage.