Etymology and English translation based on Anvaya (logical connection of words) of Maharshi Dayanad Saraswati (M.D.S)- -

(aham)=I, (hi)=by determination only, (madāya)=for pleasure, [aura]=and, (śuṣmiṇe)=appreciable force and energy for the activity in which, (samudraḥ)= ocean, (vyacaḥ) =In which various water objects are seen, [vaha]=that, (naḥ)=to us, (vā)=or, (asya)=fire named Indra, (udare)=in the midst, (enā)=hundreds or thousands, (guṇaiḥ)= by virtues, (saha)=together, (varttamānā)=are present, (yat)=which, (kriyāḥ)=actions, (santi)=are, (tāḥ)=to them, (sam)=well, (dadhe)=possess.

English Translation (K.K.V.) -

I rejoice by determination only for pleasure and commendable force and energy in the activity in which I am. For him the ocean in which various water objects are visible. The actions which are present together for hundreds or thousands by the virtues in us or the fire, named ‘Indra’. Possess them well.

TranslaTranslation of gist of the mantra by Maharshi Dayanandtion of gist of the mantra by Maharshi Dayanand -

There is simile as a figurative in this mantra. Just as in the ocean there are many types of gems and there is infinite water, in the same way, in the fire, there are many different kinds of activities. That is why, many kinds of helps can be obtained by human beings by their efforts near fire and water.