A.T. Robertson Commentary 2 Timothy 1:4

"longing to see thee, remembering thy tears, that I may be filled with joy;" — 2 Timothy 1:4 (ASV)

Night and day (νυκτος κα ημερας). Genitive of time, "by night and by day." As in 1 Thessalonians 2:9; 3:10.

Longing (επιποθων). Present active participle of επιποθεω, old word, eight times in Paul (1 Thessalonians 3:6; Php 1:8, etc.).

Remembering thy tears (μεμνημενος σου των δακρυων). Perfect middle participle of μιμνησκω, old and common verb with the genitive, only here in the Pastorals and elsewhere by Paul only in 1 Corinthians 11:2. Probably an allusion to the scene at Miletus (Acts 20:37). Cf. Acts 20:19.

That I may be filled with joy (ινα χαρας πληρωθω). Final clause with ινα and first aorist passive subjunctive of πληροω (with genitive case χαρας), a verb common with Paul (Romans 8:4; Romans 13:8).