1:20a

which He exerted in Christ: Paul is saying that God used this same power referred to in 1:19b when he raised Christ from death.

Here are some other ways to translate the word exerted :

used
-or-
showed

when He raised Him from the dead: Paul is reminding the Ephesians that it was God’s power that made Christ live again.

Here are some other ways to translate this phrase:

when he raised Christ from death (Good News Translation)
-or-
when he brought him back to life (God’s Word)

General Comment on 1:19b–20a

Here is another way to translate 1:19b–20a:

This is the same mighty power that raised Christ from the dead (New Living Translation (2004))

1:20b

seated Him at His right hand: The clause seated Him at His right hand is a figure of speech. In Jewish culture, the seat at the right-hand side of a ruler is the place of greatest honor and authority. This same figure occurs frequently in the Bible. So you should keep this figure in your translation.

If it is not clear in your translation that this is the place of honor, you may want to make this clearer in your translation. For example:

and seated him in the place of honor at God’s right hand (New Living Translation (2004))

in the heavenly realms: This is the same expression as in 1:3b. Here, however, it refers specifically to heaven where God reigns.

Here are some other ways to translate this expression:

in heaven (Contemporary English Version)
-or-
in the heavenly world (Good News Translation)

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