Assenting to the gospel

Most evangelical Christians would agree that we need to believe in and assent to the gospel. Bot HOW we assent to or believe in is of prime importance. Walter Marshall addresses this in the following excerpt from The Gospel Mystery of Sanctification:

Our assenting to, or believing the gospel, must not be forced by mere conviction of the truth, such as wicked men and devils may be brought to, when they had rather it were false.

Neither must our believing in Christ be only constrained for fear of damnation, without any hearty love and desire towards the enjoyment of Him;

but we must receive the love of the truth by relishing the goodness and excellency of it;

and we must 'account all things loss for the excellency of the knowledge of Christ Jesus our Lord, and count them but dung, that we may win Christ and be found in Him' (2 Thess. 1:10; Phil. 3:8, 9), esteeming Christ to be all our salvation and happiness (Col. 3: 11), 'in whom all fullness dwells' (Col. 1:19).

I found the idea that we must not believe in the gospel by 'mere conviction of the truth' quite shocking. My knee-jerk response would be "Why not?" As I considered it, I realized that this would be an assenting to the gospel in the same way that demons or evil men would assent to it; they are convinced of the truth of it, but do not love it.

Rather, we are called to lovingly embrace the gospel by 'relishing the goodness and excellency of it'.