A.T. Robertson Commentary Acts 1:26

"And they gave lots for them; and the lot fell upon Matthias; and he was numbered with the eleven apostles." — Acts 1:26 (ASV)

He was numbered (συνκατεψηφισθη). To the Jews the lot did not suggest gambling, but "the O.T. method of learning the will of Jehovah" (Furneaux). The two nominations made a decision necessary and they appealed to God in this way. This double compound συνκαταψηφιζω occurs here alone in the N.T. and elsewhere only in Plutarch (Them. 21) in the middle voice for condemning with others. Συνψηφιζω occurs in the middle voice in Ac 19:19 for counting up money and also in Aristophanes. Ψηφιζω with δαπανην occurs in Lu 14:28 for counting the cost and in Re 13:18 for "counting" the number of the beast. The ancients used pebbles (ψηφο) in voting, black for condemning, white (Revelation 2:17) in acquitting. Here it is used in much the same sense as καταριθμεω in verse 17.