What does a chair have to be if you are placing your faith in it?
If you place your faith in a chair to hold you, that chair must be faithful. If it is not faithful, you would go to the floor. The chair's faithfulness is what supports you, and this illustrates that Christ is faithful, which is why He can be trusted.
Les uses the chair as an illustration of faith. When people sit down, they do not analyze or inspect the chair; they simply trust it to hold them. If they are placing their faith in that chair, the chair must be faithful. If it is not faithful, they would go to the floor. In the same way, Christ has claimed to have done everything necessary, and faith is placed in that. Someday in the eternal abode, God will not say it was not what it seemed; He will say the blood of Christ is faithful. He is faithful, and that is why we can trust Him. Paul is driving at salvation through the faithfulness of the One who is faithful to keep us, because He loved us and gave Himself for us. Les also notes that it is not how much we love Him, but how much He has loved us.