So did he consider this perfection as necessary to final salvation, or not?
I'm a little rusty on the exact points of his doctrine, but so far as I understand what he believed Christian perfection to be, I don't think he believed you had to attain "Christian perfection" in order to go to heaven. But he did believe that those who did attain Christian perfection usually didn't do so until shortly before they died. Remember, Wesley never himself confesses to having experienced this very doctrine that he taught so widely.
It seems a scriptural context was lacking in his interpretation. Am I wrong?
So far as I understand Wesley's doctrine of Christian perfection, I believe he got it wrong. But that is not to say those of the Reformed persuasion got it right. I believe that we as believers are fully sanctified and attain Christian perfection the moment we get saved. That is, as Peter said, we have been given all that we need to live a life of godliness, and as Colossians says, we are complete in Him. That doesn't mean we never mess up from time to time, and that doesn't mean we don't have room to grow. Far from it, we have nothing to do but grow, even as Christ continued to grow in wisdom.
Though commonly taught throughout the history of the Church, I don't believe sanctification to be a progressive act that begins when we get saved and continues until we die. For to be sanctified is to be "set apart." And as brother Ron Bailey has pointed out before, when God created the world He didn't gradually sanctify the Sabbath day. Rather, He did it in a single moment. So I believe it is with us. We don't go from sanctification to sanctification, rather, we go from glory to glory. The object of the Christian life is not to sin less and less. Rather, the object of the Christian life is to be more and more like Jesus. Instead of trying to sin less and less, we are to seek to abound in more and more fruit.
The problem with the typical Reformed view of sanctification, and Wesley's view of sanctification, lies, imo, with a defective view of what was done in justification. The Reformed view is that when we were justified, it was merely a forensic justification that erased our guilt, though we are stained with sin. Wesley takes it another step and agrees with the forensic notion of justification, but views the justification as not only erasing our sin debt, but actually making us righteous. However, Wesley doesn't see this inner imparted righteousness as fully happening at the moment of conversion.
I would take it another step further than Wesley and say that when my sins were washed away when I was forgiven, they were entirely washed away and that I was entirely imparted with the very righteousness of Jesus Christ. I can't get any cleaner than I was made at the new birth, for the blood of Jesus made me entirely clean. My life as a Christian after that is simply a matter of me walking according to what Christ did in my heart years ago. I might stumble from time to time, but such is not because I somehow lacked the grace necessary to walk as Christ would have had me to walk.
How could he know that others had reached this point, as you said, when he was yet unable to view their hearts?
Wesley taught that one could know they were sanctified through the inner witness of the Holy Spirit. He said you could know another was entirely sanctified only because you accepted what they said, and saw them live accordingly.
Hmmm... It seems like such a complication of what I understand to be the plain gospel:
Wesley's view of sanctification is a bit difficult to understand. I had to read several works he wrote on it, and then digest a few commentaries by various theologians that attempted to summarize his view, and finally talk a few things over with my pastor before I finally came to grasp what Wesley was talking about. Part of the difficulty lies in that he had a constantly evolving vocabulary in his life that he used to preach this doctrine. And even he claims to have come to understand it only in part and gradually. But the essence of his doctrine of Christian perfection is this: That one comes to a place in their Christian walk whereby they love the Lord with ALL their heart ALL the time.
I'd highly recommend if you want to fully understand his view to pickup his book "A Plain Account of Christian Perfection," and read it through about 2 times. It's altogether about 100 pages or so. Also consider reading some other sermons of his such as "The Almost Christian," and "The Privilege of those Born Again" to give you a greater understanding of his take on things. I don't agree with everything he says, but, I think he is still a helpful read that will help refine one's own thinking.