Adam Clarke on Romans 5:3

And not only so - We are not only happy from being in this state of communion with our God, and the prospect of being eternally with him;

But we glory in tribulations also - All the sufferings we endure for the testimony of our Lord are so sanctified to us by his grace, that they become powerful instruments of increasing our happiness.

Tribulation worketh patience - Ὑπομονην, Endurance under trials, without sustaining loss or deterioration. It is a metaphor taken from refining metals. We do not speak thus from any sudden raptures, or extraordinary sensations we may have of spiritual joy: for we find that the tribulations through which we pass are the means of exercising and increasing our patience, our meek forbearance of injuries received, or persecutions experienced, on account of the Gospel.