A.T. Robertson Commentary 2 Corinthians 1:4

"who comforteth us in all our affliction, that we may be able to comfort them that are in any affliction, through the comfort wherewith we ourselves are comforted of God." — 2 Corinthians 1:4 (ASV)

In all our affliction (επ παση τη θλιψε ημων). Θλιψις is from θλιβω, to press, old and common word, as tribulation is from Latin tribulum (roller). See on Mt 13:21 and 1 Thessalonians 1:6. The English affliction is Latin afflictio from ad-fligere, to strike on.

That we may be able to comfort (εις το δυνασθα ημας παρακαλειν). Purpose clause with εις and the articular infinitive with the accusative of general reference, a common idiom. Paul here gives the purpose of affliction in the preacher's life, in any Christian's life, to qualify him for ministry to others. Otherwise it will be professional and perfunctory.

Wherewith (ης). Genitive case of the relative attracted to that of the antecedent παρακλησεως. The case of the relative here could have been either the accusative ην with the passive verb retained as in Mr 10:38 or the instrumental η. Either is perfectly good Greek (cf. Ephesians 1:6; 4:1). Personal experience of God's comfort is necessary before we can pass it on to others.