The God is the one in whom we have our faith and belief, He is like the one who can change anything from any point just depends on the belief we have toward him, for example, there was a story according to which once Saint Guru-Nanakji went to Mecca as he heard from Muslims that it is good to visit Mecca once in your Lifetime, So he went there and upon reaching the Place he got tired and slept keeping his leg toward Kaaba (unintentionally), which made one of the Qazi felt bad and he then asked Nankji that he is keeping his legs where Lord dwells, then Nanakji asked Qazi to move his leg toward the direction where God doesn't dwell, then Qazi did the same and he then realized Kaaba moved in the direction he moved Nanakji legs.
God is like the Flower with fragrance which makes us scented when we are in the vicinity to him and Real Saint is the one who devotes their life to God and they are the near resemblance to the scent which is spread by the God, So I feel they are closest to the God. According to me, it is better to be with a Real Saint then Greatest Guru as Guru can guide you to that fragrance with or without feeling that Fragrance but a Real Saint will give you that easily as they are part of him and they are more humble or giver then Guru. I am not discouraging the concept of Guru but I believe Bhakti is way much stronger then Shakti and a Real Saint learned to give unconditionally as the way he received from his God.
Nextly, Guru/s are the one who has the vision which they developed with their struggle in their life. The word Guru is made from GU which means darkness and RU which means remover/eliminator. So the faith of Guru in anyone life is to make you see what is clear for which the method can be felt right or wrong but definitely, the path will be Spiritual, He will guide you to the position from where you can start your own journey. According to my learning, there are 4 best Guru/s in our existence and they are The Sun, The Milky Way Galaxy or Adi-Shakti, The Shiva and finally Your Higher Being, you can opt any one of them to get Nirvana or Moksha but to get teaching/s from any of them you have to be evolved or at least have strength to listen your instinct/s. Difference between Guru and Teacher is that you can't be a teacher without knowing any subject but you can be Guru without knowing any subject but just having clarity in your Vision.
Lastly, Sages are those who is someone who has attained the wisdom but with the grasp of some knowledge in any specific field/s . They can be good with mathematics or astronomy or astrology or palmistry or music. Most discoveries came from sages, their life purpose is to solve the question/s arose in their mind, which later become their habit because of their good observation. For example, Ramanujam, Plato, etc.