For to this end we both labor and suffer reproach, because we have set our trust in the living God, who is the Savior of all men, especially of those who believe.
Specially of those that believe - "This is evidently designed to limit the previous remark. If it had been left there, it might have been inferred that he would “actually save” all people. But the apostle held no such doctrine, and he here teaches that salvation is “actually” limited to those who believe." (Barnes)