Slothful - Indolent, lazy, who had done nothing. God will judge people not merely for doing wrong, but for not “doing” right. See Matthew 25:45. That servant was “wicked,” because he had such an opinion of his master; he had shown that he was slothful by not making good use of the talent, Matthew 25:27.
Thou knewest ... - This should be understood, and might have been translated, as a question. If you knew that I was Such a man you ought to have acted accordingly, so as to have escaped punishment. Didst thou know that I reap, etc.? Then thou shouldst have given my money to the exchangers, etc. This is not intended to “admit” that he was such a man, but to convict the slothful servant of guilt and folly in not having been prepared to meet him.