Just like a donkey which carries the sandal wood on it's back doesn't know the importance (Or 'Value') of the sandal wood but only knows (Realises) about some weight which is put on it's back, in the same way many learned people who have studied the 'Shaastras' (Sciences) don't realise the true meaning of it and simply carry the 'weight' of the knowledge!
Deer follow deer, cows follow cows, horses follow horses (like that) fool people follow fools, and wise people go after wise. (good) friendship develops among those who have similar character and hobbies.
The sea which is only collecting the water and not giving to anyone (Rather it's water cannot be used by humans directly for drinking/cooking) is present at the lower ground level of earth and in contrast the clouds which donate the water ('jala daan') thunder from the higher altitudes.
Here the subhAshitkAra wants to emphasise that the person who does the 'daana' (One who donates- The act of giving the personal belongings) always achieves the higher place than the person who just does the 'sangraha' (collection) without the 'daana'.