‘But, O LORD of hosts, that triest’ – for ‘that triest’ read ‘that proves’. The testings of the Lord are provings to make us more faithful and more pure.
Conviction: we don't think of it as such, but it is a tremendous form of comfort from God, when we are engaged in living for him, witnessing for him, sometimes in hostile circumstances, whether in a hostile family, or business or office or wherever. This conviction that God has given us salvation and a message and an understanding: consider the value of it. It came to you with your regeneration, your illumination by the Holy Spirit. When God put this great certainty into your mind and heart that this message was true, you didn't need any apologetics to prove its veracity, its truthfulness to you. You knew it was true instinctually; you were certain of it. That is a tremendous source of comfort and assurance to all Christian people.