In the year 1639. he was one of those commissioned for the church, to treat upon the articles of pacification[63] with the king and his commissioners at Birks near Berwick, where he behaved with great prudence and candor. And when the general assembly, the same year, sat down at Edinburgh, _August_ 12, Mr. Henderson (having been the former moderator) preached to them from Acts v. 33 when _they heard that, they were cut to the heart_, &c. did towards the close of his discourse, address John earl of Traquair, his majesty's commissioner, in these words,--"We beseech your grace to see that Cæsar have his own, but let him not have what is due to God, by whom kings reign. God hath exalted your grace unto many high places, within these few years, and is still doing so. Be thankful and labour to exalt Christ's throne.----Some are exalted like Haman, some like Mordecai, &c. When the Israelites came out of Egypt, they gave all the silver and gold they had carried thence for the building of the tabernacle: in like manner, your grace must employ all your parts and endowments for the building up the church of God in this land, &c." And to the members chosen, he said, "Right honourable, worshipful, and reverend, go on in your zeal and constancy: true zeal doth not cool, but the longer it burns, the more fervent it will grow: if it shall please God that by your means the light of the gospel shall be continued, and that you have the honour of being instrumental of a blessed reformation, it shall be useful and comfortable to yourselves and your posterity. But let your zeal be always tempered with moderation; for zeal is a good servant but a bad master; like a ship that hath a full sail but no rudder. We had much need of Christian prudence, for we know what advantage some have attempted to take of us this way. For this reason let it be seen to the world, that presbytery, the government we contend for in the church, can consist very well with monarchy in the state; and thereby we shall gain the favour of our king, and God shall get the glory." After this discourse and the calling of the commissions, Traquair desired that Mr. Henderson might be continued moderator. Whether this was to corroborate his master's design, or from a regard to Mr. Henderson's abilities (as he himself professed) is not certain, but the assembly opposed this as favouring too much of the constant moderator, the first step taken of late to introduce prelacy; and no man opposed Traquair's motion more than Mr. Henderson himself, and by that means it was over-ruled.