God is both willing (John 6:39) and able to preserve us (Jude 24). To this Robert Shank responds "Our keeping ourselves in His love, in full anticipation of the mercy of our Saviour unto eternal life, is prerequisite to his safekeeping of our souls. We can trust Christ to save us, and we can trust Him to keep us; but we must trust Him." (Shank. Life in the Son. p. 279) But as Pink said: "I’m a hazard to myself, Don’t let me get me, I’m my own worst enemy". If God's not protecting us from ourselves, He's not protecting us. God saves us from the inside out.
Shank is really right about one thing and really wrong about another. We do need to trust Christ, but that's not an a prerequisite for His protection - faith is the instrument of His protection (1 Peter 1:5). Peter understood Christ's protection through experiencing trials; trials he failed but his faith failed not due to Christ's intercession (Luke 22:31-32). Shank sees Peter as a special case "that does not govern what may be true in other instances". (Shank p. 360) But the problem is twofold: 1) we see that faith is God's tool to protect us not something God requires before He will protect us and 2) if God could protect Peter through faith, He can protect us through faith. Shank grants that God is willing to protect us: "It is not the Father's will that any who come to Jesus should subsequently be lost." (Shank p. 360) So if He's willing and able, what's the hold up?
God promises not only the end (eternal life), but also the means (His protecting of our faith). He will "keep us strong" (1 Cor 1:7-9). Again, Shank puts the cart before the horse. He says: "The great promises of the faithfulness of God in performing His work of grace in our hears by His Spirit until the day of Jesus Christ all assume a corresponding faithfulness on the part of man." (Shank. p 110) But God's grace is what keeps us strong. He keeps us blameless (1 Thess 5:23-24). He strengthens us and protects us from the evil one (2 Thess 3:3). He will carry out His work in us (Phil 1:6). God doesn't wait on us to be faithful to protect us; He protects us by keeping us faithful.