A.T. Robertson Commentary Revelation 2:9

"I know thy tribulation, and thy poverty (but thou art rich), and the blasphemy of them that say they are Jews, and they art not, but are a synagogue of Satan." — Revelation 2:9 (ASV)

Thy tribulation and thy poverty (σου την θλιψιν κα πτωχειαν). Separate articles of same gender, emphasizing each item. The tribulation was probably persecution, which helped to intensify the poverty of the Christians (James 2:5; 1 Corinthians 1:26; 2 Corinthians 6:10; 2 Corinthians 8:2). In contrast with the wealthy church in Laodicea (3:17).

But thou art rich (αλλα πλουσιος ε). Parenthesis to show the spiritual riches of this church in contrast with the spiritual poverty in Laodicea (3:17), this a rich poor church, that a poor rich church. Rich in grace toward God (Luke 12:21) and in good deeds (1 Timothy 6:18). Perhaps Jews and pagans had pillaged their property (Hebrews 10:34), poor as they already were.

Blasphemy (βλασφημιαν). Reviling believers in Christ. See Mr 7:22. The precise charge by these Jews is not indicated, but see Ac 13:45.

Of them which say (εκ των λεγοντων). "From those saying" (εκ with the ablative plural of the present active articular participle of λεγω).

They are Jews (Ιουδαιους εινα εαυτους). This is the accusative of general reference and the infinitive in indirect discourse after λεγω (Acts 5:36; Acts 8:9) even though λεγοντων is here ablative (cf. 3:9), common idiom. These are actual Jews and only Jews, not Christians.

And they are not (κα ουκ εισιν). Another parenthesis like that in 2:2. These are Jews in name only, not spiritual Jews (Galatians 6:15f., Romans 2:28).

A synagogue of Satan (συναγωγη του Σατανα). In 3:9 again and note 2:13,24, serving the devil (John 8:44) instead of the Lord (Numbers 16:3; Numbers 20:4).