You are referring to a line connected with the Navkar (Namokar) Mantra, especially its mangal-gāthā part.

The traditional text (Prakrit) is:

> Eso pañcha namokkāro, savva‑pāva‑ppaṇāsano > Maṅgalāṇaṁ cha savvesiṁ, paḍhamaṁ havai maṅgalaṁ.

Your words “saraṇam maṅgalāṇam” are very close in sense to this: taking refuge (śaraṇ) in that which is supremely auspicious (maṅgal).

Simple meaning

• Eso pañcha namokkāro

This five‑fold salutation (to Arihant, Siddha, Āchārya, Upādhyāya, and all Sādhus)

• savva‑pāva‑ppaṇāsano

destroys all sinful karmas (bad tendencies, impurities).

• maṅgalāṇaṁ cha savvesiṁ

among all auspicious, holy, beneficial things,

• paḍhamaṁ havai maṅgalaṁ

this is the first, highest, most supreme auspiciousness.

Essence in very simple words

When we say this line, we are saying:

• “Taking refuge in the Navkar (bowing to these five supreme beings) is the best and most pure good thing in my life.
• It removes sins (karmas) and brings true spiritual welfare, not just worldly success.”

Digambar / Shwetambar

• Both traditions accept this same basic meaning.
• Only small differences in pronunciation of the words exist; the arth (meaning) remains identical:

Navkar is the highest mangal, and taking its śaraṇ (refuge) is the most auspicious path.

You can read a very clear explanation of Navkar Mantra and this maṅgal‑gāthā here: