As we live with the hope and anticipation of a new life, we will be tested and will experience trials and tribulations. As we rejoice during these times, God will gift us with the fruit of patience. I have copied and pasted another member's post because it is exactly how I understand this and I could not have stated it better (I hope this is ok!):
We should rejoice in our sufferings and tribulations because we are being taught patience, experience, and hope.
Perseverance is important because we go through trials, and we need to learn how to keep fighting the good fight through Jesus. The trials are continuous-they almost never stop coming.
Tried character is important because trials come to tear down our testimony, and our relationship with Jesus. So, we need to learn how to keep ourselves from doing or saying anything that will compromise our testimony, or bring a bad light to our Savior.
Hope is important because we need the hope that we have a better life coming, to keep us from getting discouraged and turn away from Jesus.