In John chapter 5 after Jesus healed the man with the infirmity, he said “…: sin no more…”. I believe in OSAS, but I have a friend that takes this to mean if you continue to sin after being saved you can lose your salvation. You have to live a holy life to keep your salvation, which I do not believe. But, what exactly did Jesus mean when he said “Behold, thou art made whole: sin no more, lest a worse thing come unto thee”, because sinning no more is just not humanly possible. Please explain.
There is no reason to interpret John 5:14 as Jesus telling this man he could lose his salvation. In John 3:16, John 5: 24, John 6:28-29, John 6:37-40 and John 10:27-30 Jesus made it clear that we are saved by believing that He came to die for our sins, that this belief is the only thing God requires of us, that He will never drive us away or lose us, and that no one can take us out of His hands. For your friend to be correct, John 5:14 would have to contradict all these other statements the Lord made.
According to some accounts of John 5:1-15, people believed that an angel would periodically come and stir up the waters of the pool of Bethesda. The first one into the pool when this happened would be healed. Translations that don’t include this explanation eliminate verse 4 from the text but may mention it as a foot note. This explains why a great number of disabled people gathered there (John 5:3).
The lesson of John 5:1-15 is that the crippled man was relying on a religious tradition for healing rather than the One who could heal him. Attributing the work of God to anyone or anything other than Him is a sin that can put us out of fellowship with God and expose us to the enemy’s mischief. This is what the Lord was telling the man to stop doing because, as you have said, it’s impossible for man to stop sinning altogether.