In other words, when an author used this grammatical device, he/she simply exhorted someone to join in with him/her in an action. He/she could exhort one to join in and help start an action that had not yet begun.
Or he/she could exhort someone to join in an action that had begun already: namely an action that was in progress and in which the author or speaker was already engaged.
In Hebrews, both kinds were used by our author. See his “Let Us Exhortation # 5” below
Heb 4:16: Let us therefore come boldly unto the throne of grace, that we may obtain mercy, and find grace to help in time of need. (KJV)
In this passage, “Let us” signifies that the author is already engaged in the action of boldly coming to the throne of Grace. He is presently coming to this throne to get some things.
First, he goes there to obtain mercy. Second, he goes there to find grace to help. Third, he goes there to get the above two things in a timely fashion, when the need arises.
By using the “Let Us Exhortation Device,” our author exhorts his readers to join in with him in an action already in progress and in which the author himself is already engaged.
He is already coming boldly into the very throne room of God himself. He is coming into that awesome room to get some things.
He does it boldly. He is not a wimp. He knows who he is. He knows what the promises are. He knows what is his.
He goes in boldly to get them. He exhorts all his readers to join in with him in this ongoing action. We should also join in with him in this ongoing action.
The blessings he sought in the throne room were promised him in the Abrahamic covenant. This Abrahamic promise included healing, prosperity and family well being in addition to salvation.
The blessings he had are also ours by grafting. Gentile Christians are included in this same Abrahamic covenant right along with the Jews. Consequently, healing, prosperity, family well being as well as salvation belong to us also.
For these reasons we can come into the throne room just as boldly as the author of Hebrews. No wonder this author used this faith building, Greek device to exhort us ( we Gentile Christians are included by grafting) to enter into this same throne room right along with him. We have the same right to enter and get what we need when we need it.
Go ahead. Go into the throne room now. If your need is healing, prosperity, family well being in addition to your salvation, go ahead and enter the throne to obtain timely. It is your God given right.