A.T. Robertson Commentary 2 Corinthians 1:23

"But I call God for a witness upon my soul, that to spare you I forbare to come unto Corinth." — 2 Corinthians 1:23 (ASV)

But I call God for a witness upon my soul (Εγω δε μαρτυρα τον θεον επικαλουμα επ την εμην ψυχην). Solemn attestation, "calling heaven to witness is frequent in literature from Homer onwards" (Plummer). Thus God is described above (cf. 1 Thessalonians 2:5,10; Romans 1:9; Galatians 1:20).

To spare you (φειδομενος υμων). Present middle participle (causal rather than final) of φειδομα, old verb, to hold back, to spare. Ablative case υμων.