Probate in Ontario, in its simplest form, is the province agreeing that the will as filed is ‘the’ will. The last one. The one in which the wishes of the deceased are explained, and the document in which the named executor(s) should follow.
Many wills require probate, but some do not. It depends on a variety of factors, which your lawyer will help you to understand. Most often, if the deceased was last to die of a couple, and held real estate and/or assets of substance (in particular assets held in a financial institution), probate will be required.
Probate requires applications to be made, assets and liabilities to be identified and valued, and fees to be paid. The benefit of probate is that it provides the executors with some protection. A probated will means that the province has endorsed the fact that this is the will, you are the executor, and you have the authority to act.
Suffice to say, that if your lawyer says you need to probate the will, then we support that.