Behold Israel after the flesh: are not they which eat of the sacrifices partakers of the altar?
Israel after the flesh - the literal, as distinguished from the spiritual Israel (Romans 2:29; Romans 9:3; Galatians 4:29).
Partakers of the altar - so of God, whose is the altar: they have fellowship in God and His worship, of which the altar is the symbol (Matthew 23:20-21).