The rules for Divine Bond, state:
At 5th level, this spirit grants the weapon a +1 enhancement bonus.
It then goes on:
For every three levels beyond 5th, the weapon gains another +1 enhancement bonus, to a maximum of +6 at 20th level. These bonuses can be added to the weapon, stacking with existing weapon bonuses to a maximum of +5, or they can be used to add any of the following weapon properties: axiomatic, brilliant energy, defending, disruption, flaming, flaming burst, holy, keen, merciful, and speed.
I'm unsure whether or not the emboldened "These" refers only to the bonuses beyond 5th level (the rules do not emphasise this word - I have done so for clarification).
In other words, at 5th level, can a paladin add one of the listed attributes to a magic weapon, or does the spirit simply add a +1 enhancement bonus?
The weapon must be magical in order to pay for the additional bonus, as clarified by:
If the weapon is not magical, at least a +1 enhancement bonus must be added before any other properties can be added.
However, I am unsure whether the additional bonuses only come into play at levels 8, 11, 14, 17 and 20.