After his return from the Westminster assembly, he was employed mostly in the public affairs of the church, until the year 1648, when he was chosen moderator to the general assembly, in which assembly several famous acts were made in favour of the covenanted work of reformation, particularly that against the unlawful engagement then made against England by the duke of Hamilton, and those of the malignant faction. In this assembly, he was one of these nominated to prosecute the treaty of uniformity in religion with England, but in a short time after this, the sickness seized him, whereof he died about the 17th of December following. Says Mr. Rutherford to him in a letter when on his death bed; "Be not heavy, the life of faith is now called for; doing was never reckoned on your accounts (though Christ in and by you hath done more then by twenty, yea, an hundred grey haired and godly pastors.) Look to that word, Gal. ii. 20. _Nevertheless, I live; yet not I, but Christ liveth in me_, &c." In his life-time he was always firmly attached to the work of reformation, and continued so to the end of his life.--For about two months before his decease, he sent a paper to the commission of the general assembly, wherein he gave faithful warning against every sin and backsliding that he then perceived to be on the growing hand both in church and state, and last of all, he emitted the following faithful testimony against association and compliance with the enemies of truth and true godliness, in these words. "Seeing now in all appearance, the time of my dissolution draweth near, although I have, in my latter will, declared my mind of public affairs, yet I have thought good to add this further testimony, that I esteem the malignant party in these kingdoms to be the seed of the Serpent, enemies to piety and presbyterial government (pretend what they will to the contrary), a generation who have not set God before them. With the malignant are to be joined the profane and scandalous, from all which, as from heresy and error, the Lord, I trust, is about to purge his church. I have often comforted myself (and still do) with the hopes of the Lord's purging this polluted land. Surely the Lord hath begun and will carry on that great work of mercy, and will purge out the rebels. I know there will be always a mixture of hypocrites, but that cannot excuse the conniving at gross and scandalous sinners, &c. I recommend to them that fear God, seriously to consider, that the holy scriptures do plainly hold forth, 1. That the helping of the enemies of God, joining or mingling with wicked men is a sin highly displeasing. 2. That this sin hath ordinarily insnared God's people into divers other sins. 3. That it hath been punished of God with grievous judgments. And, 4. That utter destruction is to be feared, when a people, after great mercies and judgments, relapse into this sin, Ezra ix. 13, 14.