"If a man does the best he can, he will be saved."
Is this what you would say? Well, have you done the best you could? Haven't you, again and again, done what you ought not to have done, and failed to do what you should have done?
"I don't pretend to be perfect."
Of course not, but this admission removes every possibility of your being saved by your doings. One sin is enough to condemn you! What is the use of saying, "If a man does the best he can," when God has told us that no one has ever done so?
The "best" that you can do is to admit that you are helpless and can do nothing to save yourself. If, from this day until the day of your death, you did not commit a single sin, you could not be saved, for sinners are not saved by what they do, but by what Christ has done for them.