Left speech radical (side-form of 言) - the indexing radical, abbreviated to two strokes. It anchors 谊 in the speech/social-interaction family with 说 speak, 话 talk, 论 discuss. Friendship is expressed through speech and dialogue, a fitting choice.
Right 宜 supplies the sound yí drifting to yì, an exact rime match. It contributes faint meaning too: 宜 means 'fitting, appropriate, harmonious,' and friendship is precisely a fitting, harmonious bond between people.
