Can someone explain to me what this statement means?

To pay all arrears of taxes to the extent that an allowance has not been granted to the purchaser on account thereof and to pay the 2015 taxes in accordance with the statement of adjustments

It means the seller of a piece of property is responsible to pay any back taxes and current year taxes, unless the purchase agreement transfers that responsibility to the purchaser. That would, according to this statement, require that the purchase price be reduced by the amount owed in taxes if the purchaser is to assume that responsibility. In other words, one way or another, the party who owned the property when the tax was due is responsible for it.