In plain words
The poet, seeing the Lord's deeds within his heart: Here is the causeway built [with the monkey army] so that Laṅkā's might would be ruined; here is the felling of Vāli, born a beast; here is the shooting that destroyed Laṅkā itself, as the bow [Śārṅga] bent and the body of Rāvaṇa in his cool garland buckled: all of these were mere sport to the one who shot those arrows [Rāma].