Basically, he proclaimed four truths: life is suffering (symptoms), there is a cause of the suffering (metaphysical truth about causality), there is a way to stop suffering (cure), and there is a path that ends all suffering (treatment plan). The path is known as “the Noble Eightfold Path”, and most of Buddhism is an explanation of the path.
The 8-fold path is a recipe. All the ingredients are interconnected. They fall into three main groupings: wisdom, ethics, and concentration. For instance, wisdom teaches us how to have the right view and right intention, but without the necessary concentration to back it up, learning wisdom is useless. The Buddha spent 35 years teaching this path.
Is it necessary that he followed this path to the end? Certainly, a Bodhisattva understands and can teach this plan of salvation without being a Buddha. This is because it is very logical. It’s a straightforward map that could have been drawn by someone with insight. You don’t have to be a abacus to solve problems using an abacus, however. It just takes more time.