Need help understanding this about the jhanas

I am reading "A Critical Analysis Of The Jhanas" And it's talking about the way to reach the first jhana. This passage below. > Block quote The Pa:isambhidāmagga explains them as follows: For one developing the first jhāna, the hindrances are abandoned by way of suppression. For one developing concentration partaking of penetration, wrong views are abandoned by way of substitution of opposites. For one developing the supramundane path that leads to their destruction, (defilements) are abandoned by way of cutting off. At the moment of fruition they are abandoned by way of tranquillization. And abandoning by deliverance is nibbāna, cessation.2 (Wr. tr.). ` The question is, isn't the first jhanas all about concentration? So why did it say if you want to reach the first jhana you must partake in abandonment by suppression, and to reach concentration you must abandoned by way of substitution of opposites. Isn't it all dedicated to concentration?