There are long list of offenses you should avoid in a spiritual life as they will hinder your spiritual progress, but an important fact is that one should be much more careful to not commit offenses against vaishnavas, since they will count much more into your karma than offenses against god. God himself is very powerful, wise, tolerant, patient etc (obviously) and therefore he does not care about offenses against him directly that much, but if someone commits offenses against his devotees he cares much more and that is why offenses against vaishnavas are worse than offenses against god, though none of both is recommended (obviously). God himself is not really harmed, but his devotees are vulnerable in cases of offenses, since their spiritual progress can be interrupted, god himself does not really have much to lose on that hand.
Related to this topic is this: https://duion.com/wisdom/you-have-serve-god-through-serving-vaishnava
This also explains why offenses against vaishnavas are worse than offenses against god, since it cuts you off from your own spiritual progress, if you cut yourself off from gods servants through committing too many offenses against them, which is the main reason offenses against vaishnavas are so bad. You will have to make up for your sins against the vaishnavas first to gain gods favor, where as god may forgive you your sins against him, but he cannot forgive you the sins against the vaishnavas, that is up to them to forgive you.