That’s like saying, “Why should I bother with ever talking with my parents when they’ll give me my food and bed and toys whether I do or not?” By talking with our parents, we get to know them better and love them more, and we learn what their will is. We in turn do their will, if we’re good, and make both them and ourselves the happier for it. We make their many tasks the easier by participating in their will rather than leaving it all to them or resisting it outright.
God has made us “co-creators with him,” participants in the fulfillment of his will here on Earth. If we shirk our responsibility to do good by praying according to God’s will, then good won’t be done because we will have failed to fulfill our duty as “co-creators.”
By praying against abortion, we can save lives. We are taught to pray in the Our Father, “thy kingdom come, thy will be done.” We are praying that God’s will shall be done. Even Jesus prays to the Father.
God has a will for everyone and the devil does too. God turns people over to the devil when they reject God’s ways. So we pray in accord with God’s will against the power of the enemy, thus saving lives and becoming part of the fulfillment of God’s will on Earth. It is a glorious calling we all have.