I stands for irresistible grace. Left to ourselves we resist the grace of God. But when God works in our hearts, regenerating us and creating a renewed will within, then what was undesirable before becomes highly desirable, and we run to Jesus just as previously we ran away from Him. Fallen sinners do resist God's grace, but His regenerating grace is effectual. It overcomes sin and accomplishes God's purpose.
P stands for perseverance of the saints.
God perseveres with us, keeping us from falling away, as we would certainly do if He were not with us. But because He perseveres we also persevere. In fact, perseverance is the ultimate proof of election. We persevere because God preserves us from full and final falling away from Him. The Cultural Mandate.