Note this assumes 3 cells per as a pattern:
Office 365/2019:
=TEXTJOIN(", ",TRUE,INDEX(A:A,(ROW($ZZ1)-1)*3+1):INDEX(A:A,(ROW($ZZ1)-1)*3+3))
Older:
=IF(INDEX(A:A,(ROW($ZZ1)-1)*3+1)<>"",INDEX(A:A,(ROW($ZZ1)-1)*3+1) & ", " & INDEX(A:A,(ROW($ZZ1)-1)*3+2) & ", " & INDEX(A:A,(ROW($ZZ1)-1)*3+3),"")
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…