The last part of Clark says this:
Denying the Lord that bought them - It is not certain whether God the Father be intended here, or our Lord Jesus Christ; for God is said to have purchased the Israelites, Exo_15:16, and to be the Father that had bought them, Deu_32:6, and the words may refer to these or such like passages; or they may point out Jesus Christ, who had bought them with his blood; and the heresies, or dangerous opinions, may mean such as opposed the Divinity of our Lord, or his meritorious and sacrificial death, or such opinions as bring upon those who hold them swift destruction. It seems, however, more natural to understand the Lord that bought them as applying to Christ, than otherwise; and if so, this is another proof, among many,
1. That none can be saved but by Jesus Christ.
2. That through their own wickedness some may perish for whom Christ died.