Why do I need a strong will and determination?

Because knowing God's Will and doing God's Will are not the same thing.

Many people know what is right but fail to do it. The Christian life requires more than knowledge. It requires the willingness to choose what is good, even when it is difficult, unpopular or costly.

Jesus Himself says: “If any want to become my followers, let them deny themselves and take up their cross and follow me.” — Matthew 16:24

The lay apostolate places us in situations similar to carrying a cross.

These situations demand courage, perseverance and fidelity.

The Lord warned us: “If the world hates you, be aware that it hated me before it hated you. If you belonged to the world, the world would love you as its own. Because you do not belong to the world, but I have chosen you out of the world—therefore the world hates you. Remember the word that I said to you, ‘Servants are not greater than their master.’ If they persecuted me, they will persecute you; if they kept my word, they will keep yours also.” — John 15: 18

One with a weak desire and no determination to follow Christ will abandons the good they are trying to do when it becomes inconvenient or challenged.

The question is not only whether we know God's Will, but whether we are prepared to live it, no matter what, even if it means losing our life. Losing our life is not always literal. Many times, it simply means giving up our dreams, ambitions, comfort for the sake of God’s Will.