Bottom line: These are faithful sayings: suffering leads to reigning; spiritual exercising leads to godliness; trusting Jesus saves sinners.

The Apostle Paul in writing to Timothy shared with him some statements of truth that he called "faithful sayings," i.e. "Timothy, you can trust what I am saying is true." We might say it this way today: "Timothy, you can count on it; you can take it to the bank."

Jesus came into this world to save sinners. He paid the sinner's penalty and provided for the saint's victory.
Exercising spiritually leads to godliness in us and has benefit in the this life and the life to come.
Suffering for the cause of Christ and/or the plan of Christ will lead to reigning with Christ. Suffering has a promise reigning. It's a paradox, but it is true.