The proof (thn dokimhn). "The test" as of metals ( 2 Corinthians 2:9 ; 2 Corinthians 9:13 ). Three times they had seen Timothy ( Acts 16:13 ; Acts 19:22 ; Acts 20:3 ). With me (sun emoi). Paul's delicacy of feeling made him use sun rather than emoi alone. Timothy did not serve Paul. In furtherance of (ei). See Philippians 1:5 for this use of ei.