Lu 7:7 ...say the word, and my servant will be healed.
Lu 7:9 When Jesus heard these things, he marveled at him, and turned and said to the multitude who followed him, "I tell you, I have not found such great faith, no, not in Israel."
The centurion in this story is a great man of faith. His dear servant was dying and he was helpless to do something about it. But he knew the Lord Jesus Christ and all he needed from Him is His word about the situation.
To him, all the Lord had to do was utter the words and his faith will latch on it (Faith is taking God at His Word). He knew that the Lord's Word is the surest thing in the universe. Behind the Word of God is the God of the Word who is all-powerful and one who cannot lie. When He utters something, you can be sure that it is as good as done. You just wait and see.
The result? His servant was healed.
In the same way, we are all spiritually sick and ready to perish forever. But God has a word for us: "Jesus Christ died for your sins and rose from the dead."
If we just take Him at His word, trust in this good news of a message, we will enter into the good of this message and salvation will be effected in our lives.