sich erfreuen an
to take delight in
To feel joy or pleasure in something; to enjoy something.
Im Frühling erfreue ich mich an den blühenden Blumen im Garten.
In spring, I take delight in the blooming flowers in the garden.

to delight
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to take delight in
To feel joy or pleasure in something; to enjoy something.
Im Frühling erfreue ich mich an den blühenden Blumen im Garten.
In spring, I take delight in the blooming flowers in the garden.

'Erfreuen' (to delight) is an inseparable verb made up of the prefix 'er-' and the verb 'freuen' (to be happy / to please). The root of the word is 'die Freude' (joy).
Sein unerwarteter Besuch hat uns sehr erfreut.
His unexpected visit delighted us very much.
The verb has two grammatical patterns: when you yourself feel joy, you use it reflexively with the preposition 'an' + dative. When you bring joy to someone else, you use it transitively with an accusative object.
Sie erfreut sich an den kleinen Dingen des Lebens.
She takes delight in the little things in life.
'Erfreuen' (to delight) is part of an elevated, rather formal style of language. In everyday speech, people would usually use 'sich freuen über' (to be happy about) or 'jemandem eine Freude machen' (to make someone happy).
Wir erfreuen uns bester Gesundheit.
We enjoy the best of health.
The expression 'sich großer Beliebtheit erfreuen' (to enjoy great popularity) is a formal way of saying that something is very popular. The adjective before 'Beliebtheit' can vary, e.g., 'wachsender' (growing) or 'ungebrochener' (unbroken) popularity.
Podcasts erfreuen sich seit Jahren wachsender Beliebtheit.
Podcasts have enjoyed growing popularity for years.
to look forward / to be pleased
'freuen' and 'erfreuen' can be very similar when they are about joy. 'sich freuen über' is the normal and common form in everyday language. 'sich erfreuen an' means almost the same as taking pleasure in something, but it sounds more elevated or formal. 'Das freut mich' and 'Das erfreut mich' also mean similar things, but 'Das freut mich' is much more natural in conversation. Learners may confuse the words because they look almost the same. The important thing is the form: you say 'man freut sich über etwas' (one is pleased about something), but 'man erfreut sich an etwas' (one takes delight in something). There are also fixed formal phrases such as 'sich großer Beliebtheit erfreuen' (to enjoy great popularity).

Im Park erfreuen sich viele Besucher an den Blumen.
In the park, many visitors take delight in the flowers.
Der Kunde freut sich über die schnelle Hilfe.
The customer is pleased about the quick help.