While it's certainly true that you should listen carefully to your conscience, there is also a definite danger in this area of developing an over-sensitive conscience. It
could be your conscience prodding you that you are wasting time; it
could be that you are becoming over-sensitive in a way that is actually a temptation.
The Bible nowhere says that all our time and energy should be spent on 'spiritual' matters; on the contrary, the creation is given for our enjoyment as well as for us to govern it.
While neither watching sports nor computer games are directly creations of God, 1 Timothy 4:4 is a critical verse in regulating our consciences:
For everything created by God is good, and nothing is to be rejected if it is received with thanksgiving
If something is not forbidden by scripture, and you can do it with appreciative gladness towards God, which means that it doesn't have a negative effect on us spiritually or morally, then we should feel free to do it within appropriate measure - and certainly not bind the consciences of others on that matter.
Especially when one is young or first getting into reformed theology, there's a real danger of becoming legalistic and over-sensitive in conscience in this area.
All that said, that doesn't mean you should definitely spend loads of time doing these two things. How much and whether you should do them is a complicated question, and one not answered by a simple yes/no. It takes wisdom, in your particular situation, taking account of yourself, your friends, your needs, obligations and opportunities.
Some parameters to keep in mind:
- The obvious: are you completing your responsibilities? Have you studied hard for a decent amount of time, got your work in on time? Have you been to church, read your Bible, prayed, considered what ways you can love your neighbour and serve your God today? Talked with your family?
- Have you also completed those tasks that keep you fit and healthy and functioning well for the long term? Have you been outside, exercised, eaten properly, maybe read a stimulating and thought-provoking book? Have you spent some time with friends?
- You do need rest: do these activities genuinely rest you, so that you are refreshed and relaxed, able to serve God and study better?
- You do need friendship: do these activities give you opportunities to build relationships (both deeper ones with Christians, and evangelistic opportunities with non-Christians)?
- Are these activities exposing you to temptations that are unhelpful - e.g.
- is sports-watching taking too much time, encouraging laziness?
- is it encouraging too much socialising with people who are a bad influence?
- Is a sports team becoming an idol?
- Are your particular computer games too violent/sexualised in a way that is bad for you?
- Do those games tempt you into wasting time when you should be working?
- Do they actually overstimulate your system so that you can't relax/read books/concentrate after doing them.
There's a real difference between the nagging feelings you get when doing something... it could be your conscience reminding you that you should be doing something
particular that you have failed to do. If so, go do it. If, on the other hand, it's a generic sense that this activity isn't 'spiritual' enough... then there's a danger that you are actually hyper-spiritualising things in a way that's unhelpful. Looking at your post, I'd pick out these lines in particular:
How is the Christian to engage with activities that aren't regarded as inherently fruitful
We are
supposed to engage in unfruitful activities. That's what a lot of rest is. That's what Ecclesiastes is saying when it is good to eat and drink and enjoy what God has given. To think you can be fruitful all the time is to elevate yourself above mere creatureliness. To be dependent, to enjoy without always producing, is a
duty. Done rightly, it reminds us of our dependence on God himself.
there lingers a feeling that I'm forsaking joy everlasting for a transient sensation (2 Cor. 4:18)
This verse is obviously talking about present sufferings, not present enjoyments. Even if it was, Paul wasn't saying that you shouldn't deal with these things at all - but that our ultimate focus, goal and purpose is heavenly.
squandering the blessing time He has give me (Eph 5:16) when I participate in such. If my view does hold any untruth, how are we to interact with verses such as Josh. 1:8 and Ps. 1:2, finding the balance between direct correspondence with God, i. e. prayer (Jn. 16:24), dwelling in Scripture, with such things that hold no benefit except for our own, temporary benefit?
'Our own temporary benefit' is actually important. We are temporary creatures. We just need to put God and other people first.
I acknowledge that we will need abundant grace even after the good work begun in us has been wrought unto completion, but should indulging in more "lax" activities been seen as something we even need repentance for, or is it a means by which God providentially blesses us with emotional and mental rejuvenation?
Again, it depends what you mean by 'lax', but I see no indication in scripture that
all our time should be either work or spiritual.
Now all that needs to be thought about before the particular activities you've mentioned: my
personal feeling is that these aren't the most refreshing or joy-bringing forms of recreation you could be involved in. It's probably better to
do sport than watch it; and PC games can certainly swallow much time without bringing that much real joy. But
if you think that and cut them out make sure that you find good alternative rest that is more refreshing. And don't cut yourself off from all friendship to do it.
Personally I hate watching sport, and it
feels like wasted time to me: but I have to acknowledge that many far more godly men than I love watching it and have great friendships that include doing this together.
My own experience is that I am sometimes tempted to over-spiritualise my use of time: to feed myself constantly with books and prayer. I actually burn out pretty quickly when I do this. We are not angels, able to manage constant spiritual focus, but embodied beings. Trying to live like an angel is the error that a lot of early monastics fell into; it ultimately becomes a form of works-righteousness. As a student you will equally need to guard yourself against the temptation of laziness - don't fall for either extreme, but spend time in prayer and with wise friends or a pastor working these things through and trying to find a good, healthy balance.